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These studies show synthesis of triphasic size- and Janus balance (JB)-tunable nanoparticles (JNPs) utilizing a two-step emulsion polymerization of pentafluorostyrene (PFS) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) and n-butyl acrylate (nBA) in the presence of poly(methyl methacrylate (MMA)/nBA) nanoparticle seeds. Each JNP consists of three phase-separated copolymers: p(MMA/nBA) core, temperature, and pH-responsive (p(DMAEMA/nBA)) phase capable of reversible size and shape changes, and shape-adoptable (p(PFS/nBA)) phase. Due to built-in second-order lower critical solution temperature (II-LCST) transition of p(DMAEMA/nBA) copolymer, macromolecular segments collapse when temperature increases from 30 to 45 °C, resulting in size and shape changes. The p(DMAEMA/nBA) and p(MMA/nBA) phases within each JNP assume concave, flat, or convex shapes, forcing p(PFS/nBA) phase to adopt convex, planar, or concave interfacial curvatures, respectively. As a result, the JB can be tuned from 3.78 to 0.72. The prese...

These studies show covalent attachment of multilayers (CAM) to chemically alter surfaces to achieve pH switchable antimicrobial and anticoagulant properties. Polyethylene (PE), poly(tetrafluoroethylene) (PTFE), and silicon (Si) surfaces were functionalized by tethering pH-responsive “switching” polyelectrolytes consisting of poly(2-vinyl pyridine) (P2VP) and poly(acrylic acid) (PAA) terminated with NH2 and COOH groups, respectively. At pH 5.5, they collapse while the PAA segments are expanded. The presence of terminal NH2 or COOH moieties on P2VP and PAA, respectively, facilitated the opportunity for covalently bonding ampicillin (AMP) and heparin (HEP) to both polyelectrolyte chains. Such surfaces, when exposed to S. aureus, inhibit the growth of microbial films (AMP) as well as anticoagulant properties (HEP). Comparison of “dynamic” pH dependent surfaces developed in these studies with “static” surfaces terminated with (AMP) entities shows significant enhancement in the longevity of surface activity against microbial film formation.

Formation of heterogeneous and controllable surface patterns on polymeric materials containing antimicrobial and anticoagulant components represent an attractive way of maintaining synthetic materials “clean” from adverse bio-activities. The primary surface “contaminants” are microbial films as well as blood coagulation, both affecting not only performance of internal or external devices, but often exhibiting detrimental effects on patients. In an effort to simultaneously inhibit formation of microbial films and surface blood coagulation multifunctional assemblies containing streptavidin (STR)–biotin bioconjugates were developed on poly(tetrafluoroethylene) (PTFE) surfaces. Using STR conjugated to a biotin-functionalized PTFE surface, spatially controlled micro-patterning was produced by grafting biotinylated polyethylene glycol (B-PEG) to COOH modified PTFE (MA-PTFE), followed by inkjet micro-printing of biotinylated ampicillin (B-AM) and biotinylated heparin (B-HP) molecules. These surfaces exhibit simultaneous antimicrobial and anticoagulant attributes manifested by “zone of inhibition” and anticoagulant measurements. Quantitative spectroscopic analysis revealed that the required surface density of COOH groups on PTFE is 2.94 × 10−7 g cm−2, and B-PEG and STR densities of 9.2 × 10−8 g cm−2 and 3.5 × 10−8 g cm−2, respectively, are sufficient to achieve simultaneous antimicrobial and anticoagulant responses. These studies also showed that the force required to remove STR–biotin conjugates attached to PTFE surfaces measured by atomic force microscopy is approximately 1090 pN, thus providing desirable surface mechanical stability.

This chapter summarizes selective advances of stimuli-response nanomaterials and consists of two sections: responsive nanoparticles and responsive nanowires and nanotubes. Stimuli-responsive nanomaterials play an important role in modern materials’ design and offer numerous opportunities for future technological advances. Numerous studies published as early as 1950s have reported the synthesis of colloidal nanomaterials, which primarily focused on spherical colloidal nanoparticles known as latexes. Formation of anisotropic stimuli-responsive nanomaterials is accomplished by molecular design of copolymer blocks that in specific environments will self-assemble to form anisotropic shapes. Multilayers of nanotube-forming phospholipid templates that consist of thermally responsive polymers can serve as templates with tunable diameter and wall thickness. A general method to fabricate these nanotubules is to incorporate polymerizable thermal-responsive monomers into the hydrophobic area of phospholipid template.

Simple routes to self-healing Biology provides many routes for self-healing or repair, but this trait is hard to endow into engineering materials. Although self-repair has been demonstrated for some polymers, it usually required specialized monomers. Urban et al. demonstrate that for a very narrow range of compositions, simple vinyl polymers based on methyl methacrylate and n -butyl acrylate show repeatable self-healing properties (see the Perspective by Sumerlin). A key characteristic of this system is that it relies on van der Waals interactions rather than the reformation of hydrogen or covalent bonds for repair. Science , this issue p. 220 ; see also p. 150

Although dipolar forces between copolymer chains are relatively weak, they result in ubiquitous inter‐ and/or intramolecular interactions which are particularly critical in achieving the mechanical integrity of polymeric materials. In this study, a route is developed to obtain self‐healable properties in thermoplastic copolymers that rely on noncovalent dipolar interactions present in essentially all macromolecules and particularly fluorine‐containing copolymers. The combination of dipolar interactions between C─F and C═O bonds as well as CH2/CH3 entities facilitates self‐healing without external intervention. The presence of dipole‐dipole, dipole‐induced dipole, and induced‐dipole induced dipole interactions leads to a viscoelastic response that controls macroscopic autonomous multicycle self‐healing of fluorinated copolymers under ambient conditions. Energetically favorable dipolar forces attributed to monomer sequence and monomer molar ratios induces desirable copolymer tacticities, enabling entropic energy recovery stored during mechanical damage. The use of dipolar forces instead of chemical or physical modifications not only eliminates additional alternations enabling multiple damage‐repair cycles but also provides further opportunity for designing self‐healable commodity thermoplastics. These materials may offer numerous applications, ranging from the use in electronics, ion batteries, H2 fuel dispense hoses to self‐healable pet toys, packaging, paints and coatings, and many others., Fluorine‐containing acrylic‐based copolymers that rely on noncovalent dipolar interactions between CH2/CH3 entities as well as C─F and C═O bonds result in a viscoelastic response leading to macroscopic autonomous self‐healing. The presence of favorable dipolar forces is attributed to monomer sequences and monomer molar ratios facilitating desirable copolymer tacticity, enabling entropic energy storage, and recovery during multiple damage‐repair cycles.

Living organisms utilize metabolic processes to achieve adaptive, reproductive, and self-healing functions, which require dynamic and precise control of sequential chemical events. Since traditional synthetic materials do not possess these functions, there is an ongoing quest for the development of self-healing attributes. This study reports self-healing of crosslinked polyurethane networks by damage-induced formation of primary amines. Deliberately modified with methyl α-D-glucopyranoside (MGP) and catalyzed by zinc acetate (Zn(OAc)2), polyurethane (PUR) networks are capable of restoring mechanical properties upon mechanical damage. Self-repair is initially driven by entropic shape recovery facilitating interfacial contacts in damaged areas, followed by covalent reformation of cleaved bonds. Amine functionalities resulting from mechanical damage facilitate covalent re-bonding to form urea linkages responsible for recovery of mechanical properties.

Self-healing polymeric materials that can spontaneously repair in a perpetual manner are highly appealing to address safety and restoration issues in different key applications. Usually built from reversible moieties that require to be activated using, for example, temperature, light, or pH changes, most of these self-healing materials rely on energy-demanding processes and/or external interventions to promote self-healing. In this work, we propose to exploit rapid dynamic exchanges between urea-based moieties and moisture as an alternative to promote local and spontaneous healing responses to damage using atmospheric moisture as an external stimulus. Non-hygroscopic urea-based polyurethanes with repetitive moisture-induced healing abilities at different degrees of humidity were thus designed through coupling reactions with non-hygroscopic polypropylene glycol and urea moieties. As supported by density functional theory (DFT) calculations coupled to local FTIR experimental studies, we furthermore established that the healing mechanism is ultimately related to the formation of water-urea clusters. Obviously, this work represents a platform for designing more advanced spontaneous self-healing materials beyond the present study, which hold promise for use in a wide range of technological applications.

In this study, we demonstrated that carbon films with nanoscale roughness and controllable thickness can be produced by high temperature treatment of the polyacrylonitrile (PAN) film fabricated through dip-coating from 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) solution. Specifically, ultrasmooth (root mean squared average roughness between 1 and 3 nm), crack-free carbon films were produced. In our procedure, the PAN films were first deposited onto a silicon wafer by conventional dip-coating process. Next, the films were stabilized at 230 °C in air and then carbonized at 1000 °C in an inert atmosphere. Raman spectroscopy indicated that after carbonization the films with ordered graphite structure as well as disordered phase were obtained. The same basic procedure was used to form porous carbon films with tunable porous structures when PAN and polyethylene oxide (PEO) blend was used instead of PAN only. In PAN/PEO blended films, PEO functioned as the pore initiation agent and resulted in carbon films whose pore diameter could be varied from hundreds of nanometers to micrometers. The carbon films (solid and porous) obtained in this study exhibit relatively high electrical conductivity. We expect that the method reported here can be employed for scalable manufacturing of ultrasmooth as well as porous carbon films.

Ultrahigh molecular weight (>106 g/mol) amphiphilic block copolymers were synthesized using one-step surfactant-free heterogeneous radical polymerization (SFHRP). The polymerization initially involves formation of water-soluble homopolymer blocks, followed by copolymerization of a hydrophobic monomer, resulting in ultrahigh molecular weight block copolymers. Facilitating heterogeneous reaction conditions and continuous supply of an initiator controls the process. Using this synthetic approach, we synthesized amphiphilic block copolymers of poly(2-(N,N-dimethylamino)ethyl methacrylate)-block-poly(n-butyl acrylate) (pDMAEMA-b-pnBA), pDMAEMA-block-p(tert-butyl acrylate) (pDMAEMA-b-tBA), and pDMAEMA-block-polystyrene (pDMAEMA-b-pSt) with molecular weights of 1.98 × 106, 1.18 × 106, and 0.91 × 106 g/mol, respectively. These ultrahigh molecular weight block copolymers can self-assemble in nonpolar solvents to form thermochromic inverse polymeric micelles as well as other shapes and exhibit many potential applic...

Sugar moieties were incorporated into cross-linked polyurethane (PUR) networks in an effort to achieve self-repairing in the presence of atmospheric carbon dioxide (CO2) and water (H2O). When methyl-α-D-glucopyranoside (MGP) molecules are reacted with hexamethylene diisocyanate trimer (HDI) and polyethylene glycol (PEG) to form cross-linked MGP-polyurethane (PUR) networks, these materials are capable of self-repairing in air. This process requires atmospheric amounts of CO2 and H2O, thus resembling plant behavior of carbon fixation during the photosynthesis cycle. Molecular processes responsible for this unique self-repair process involve physical diffusion of cleaved network segments as well as the formation of carbonate and urethane linkages. Unlike plants, MGP-PUR networks require no photo-initiated reactions, and they are thus capable of repair in darkness under atmospheric conditions.

In this study we developed simple reactions that combined microwave plasma reactions in the presence of maleic anhydride with alkyne click chemistries to achieve a platform for unlimited possibilities for further surface modifications of aliphatic polymer surfaces. Using this approach, we covalently attached ampicillin (AMP) to polyethylene (PE) and polypropylene (PP) substrates. As a result, high efficacy against microbial film formation, manifested by efficient antimicrobial activity against S. aureus with a 97-99.8% decrease of bacterial growth, was achieved. This simple and clean process allows functionalization of any polymeric substrate without adverse effects on bulk polymer properties.

This study focuses on the development of facile polyethylenimine–copper (C2H5N–Cu) supramolecular polymer networks which upon mechanical damage are capable of reversible UV-induced self-repairs by the reformation of Cu–N coordination bonds. The chemical changes responsible for self-healing that leads to network remodeling include the formation of C2H5N–Cu complexes which, upon UV absorption, induce charge transfer between σ(N) bonding and dx2–y2(Cu) antibonding orbitals. The primary structural component responsible for network remodeling is the C2H5N–Cu coordination complex center that, upon UV exposure, undergoes square-planar-to-tetrahedral (D4h → Td) transition. The energy difference between dx2–y2 and dxz/yz orbitals during process change decreases significantly, enabling the σ(N) → dx2–y2(Cu) charge transfer and leading to energetically favorable Cu–N geometries. Manifested by virtually no temperature changes during UV-initiated self-healing, a unique feature of this network is the high efficiency of the damage–repair cycle resulting from the reversible conversion of electromagnetic radiation to chemical energy.

Polymeric nanowires that consist of ultrahigh molecular weight block copolymers were instantaneously prepared via one-step surfactant-free heterogeneous radical polymerization (HRP). Under heterogeneous reaction and initiator-starvation conditions, the sequential copolymerization of hydrophilic and hydrophobic monomers facilitates the formation of amphiphilic ultrahigh molecular weight block copolymers, which instantaneously assemble to polymeric nanowires. As polymerization progresses, initially formed nanoparticles exhibit the directional growth due to localized repulsive forces of hydrophilic blocks and confinement of the hydrophobic blocks that adopt favorable high aspect ratio nanowire morphologies. Using one-step synthetic approach that requires only four ingredients (water as a solvent, two polymerizable monomers (one hydrophilic and one hydrophobic), and water-soluble initiator), block copolymer nanowires ∼70 nm in diameter and hundreds of microns in length are instantaneously grown. For example, when 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) and styrene (St) were copolymerized, high aspect ratio nanowires consist of ultrahigh (10(6) g/mol) molecular weight pDMAEMA-b-St block copolymers and the presence of temperature responsive pDMAEMA blocks facilitates nanowire diameter changes as a function of temperature. These morphologies may serve as structural components of the higher order biological constructs at micro and larger length scales, ranging from single strand nanowires to engineered biomolecular networks capable of responding to diverse and transient environmental signals, and capable of dimensional changes triggered by external stimuli.

Although the last decade has brought self-healing materials to the forefront of scientific interests, combining repair and sensing attributes into one material entity have not been addressed. These studies report the development of poly(methyl methacrylate/n-butylacrylate/2-[(1,3,3-trimethyl-1,3-dihydrospiro[indole-2,3′-naphtho[2,1-b][1,4]oxazin]-5-yl)amino]ethyl-2-methylacrylate) [p(MMA/nBA/SNO)] copolymer films that upon mechanical scratch undergo color changes from clear to red in the damaged area, but upon exposure to sunlight, temperature and/or acidic vapors, the damaged area is self-repaired and the initial colorless appearance is recovered. The process is reversible and driven by the ring-opening-closure of spironapthoxazine (SNO) segments to form merocyanine (MC), which are recovered back to the SNO form. Upon mechanical damage, SNO segments of the neighboring copolymer segments form inter-molecular H-bonding that stabilizes copolymer backbone, that remains in an extended conformation. External stimuli, such as light, temperature, or acidic environments cause a dissociation of the H-bonded MC pairs, which are converted back to SNO. This process is associated with the p(MMA/nBA/SNO) backbone collapse, thus pulling entangled neighboring copolymers to fill removed mass and repair a scratch. Mechanical nano-indentation analysis combined with molecular modeling and spectroscopic measurements confirm this behavior. The enclosed video clip illustrates molecular repair processes induced by visible light monitored by in situRaman imaging spectroscopy. These materials may find numerous future applications, where coupling of simultaneous color changes and reversible self-repair responses may lead to new technological paradigms.

Materials with the ability of dimensional changes on demand exhibit many potential applications ranging from adaptive composites that mimic biological functions under extreme conditions to microfluidics or neural implants to stimulate components of the nervous systems. These studies show the synthesis of temperature-induced reversibly expandable nanotubes that were prepared by polymerization of N-isopropylacrylamide (NIPAAM) in the presence of biologically active 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine (DC8,9PC) diacetylenic phospholipids (PL). As a result, thermally responsive poly-NIPAM-phospholipid nanotubes (PNNTs) were prepared. Polymerization reactions occur within hydrophilic regions of PL bilayers, whereas PL hydrophobic zones facilitate transport and supply of the monomer for polymerization. The unique feature of PNNTs is that, above 37 °C, the outer diameter (OD) as well as the wall thickness (WT) shrink by 20 and 55%, respectively, whereas the inner diameter (ID) increases by...

Cilia are wavy hair-like structures that extend outward from surfaces of various organisms. They are classified into two general categories, primary cilia, which exhibit sensing attributes, and motile cilia, which exert mechanical forces. A new poly(2-(N,N-dimethylamino)ethyl methacrylate-co-n-butyl acrylate-co-N,N-(dimethylamino) azobenzene acrylamide) (p(DMAEMA/nBA/ DMAAZOAm) copolymer is prepared using colloidal synthesis, which, upon coalescence, form films capable of generating surfaces with cilia-like features. While film morphological features allow the formation of wavy whiskers, the chemical composition ofthe copolymer facilitates chemical, thermal, and electromagnetic responses manifested by simultaneous shape and color changes as well as excitation wavelength dependent fluorescence. These studies demonstrate that synthetically produced polymeric films can exhibit combined thermal, chemical, and electromagnetic sensing leading to locomotive and color responses, which may find numerous applications in sensing devices, intelligent actuators, defensive mechanisms, and others.

In an effort to elucidate the origin of stimuli-responsive (TSR) transitions and correlate them to the glass transition temperature (Tg), poly(N-acryloyl-N′-propylpiperazine-co-2-ethoxyethyl methacrylate) (p(AcrNPP/EEMA)), poly(N-vinylcaprolactam-co-n-butyl acrylate) (p(VCl/nBA)), poly(N-isopropyl methacrylamide-co-n-butyl acrylate) (p(NIPMAm/nBA)), and poly(2-(N,N′-dimethylamino)ethyl methacrylate-co-n-butyl acrylate) (p(DMAEMA/nBA)) colloidal dispersions were synthesized, which upon coalescence form solid films. These studies showed that molecular rearrangements responsible for the TSR transitions are attributed to the backbone buckling and collapse of stimuli-responsive components. Based on empirical data, the relationship between Tg and TSR was established: log(V1/V2) = (P1(TSR − Tg))/(P2 + (TSR − Tg)), where the V1 and V2 are the copolymer total volumes below and above the TSR, respectively, Tg is the glass transition temperature of the copolymer, and P1 and P2 are the fraction of the free volume (ff...

A poly(n-butyl acrylate)-based star polymer, polyEGDA-(polyBA)n, was synthesized by atom transfer radical polymerization using a modified core-first method. Further polymerization of a disulfide (SS) cross-linking agent bis(2-methacryloyloxyethyl) disulfide from the arm end produced a SS cross-linked star polymer. The disulfide functionality could be cleaved via reducing reactions, generating individual stars containing SH groups at the chain ends. The transformation between SS cross-linked star and SH-star was reversible via repetitive reduction and oxidation. Dynamic light scattering measurements showed that the average diameter of the cleaved star polymer was around 20 nm. The dynamic mechanical properties of these star copolymers were characterized through examination of the temperature dependencies of their shear moduli. The results showed that SS-functionalized star polymers respond to reduction−oxidation conditions, indicating that the disulfide bonds do cleave and re-form. These stimuli responsive...

While aqueous phase colloidal synthesis of F-containing dispersions is often restricted by low solubility and surface tension of monomers, the use of bioactive dispersing agents, such as phospholipids, may alleviate these problems. Using 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), we copolymerized heptafluorobutyl methacrylate (FBMA), heptafluorobutyl acrylate (FBA), heptadecafluorodecyl methacrylate (FMA), heptadecafluorodecyl acrylate (FA) with methyl methacrylate (MMA) and n-butyl acrylate (nBA) monomers which resulted in the formation of stable nonspherical colloidal dispersions that contain up to 15% (w/w) of the fluoropolymer (FP) phase. These studies report for the first time an aqueous phase FP colloidal dispersion synthesis without the use of fluoro-dispersing agents. Experimentally determined by transmission electron microscopy (TEM) particle phase-separated morphologies consist of the FP phase that polymerize on the surface of p-MMA/nBA core particles. Thermodynamic molecular modeling sim...

While aqueous phase colloidal synthesis of F-containing dispersions is often restricted by low solubility and surface tension of monomers, the use of bioactive dispersing agents, such as phospholipids, may alleviate these problems. Using 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), we copolymerized heptafluorobutyl methacrylate (FBMA), heptafluorobutyl acrylate (FBA), heptadecafluorodecyl methacrylate (FMA), heptadecafluorodecyl acrylate (FA) with methyl methacrylate (MMA) and n-butyl acrylate (nBA) monomers which resulted in the formation of stable nonspherical colloidal dispersions that contain up to 15% (w/w) of the fluoropolymer (FP) phase. These studies report for the first time an aqueous phase FP colloidal dispersion synthesis without the use of fluoro-dispersing agents. Experimentally determined by transmission electron microscopy (TEM) particle phase-separated morphologies consist of the FP phase that polymerize on the surface of p-MMA/nBA core particles. Thermodynamic molecular modeling sim...

A new family of water-dispersible colloidal particles composed of poly(methyl methacrylate/n-butyl acrylate/pentafluorostyrene/poly(ethylene glycol) dimethacrylate) (p-MMA/nBA/PFS/PEG) copolymers w...

Recent advances in developments of anticoagulant, antifouling, and antimicrobial polymeric surfaces with the focus on surface modifications of polymeric materials as well as the influence of nanosize materials on interactions with biological systems are discussed. Controllable surface modifications using microwave plasma reactions in the presence of maleic anhydride provides a platform for attaching acid groups to inert polymeric surfaces which serves as a reactive anchor for further reactions. To effectively attach bioactive species inhibiting interactions with biological systems it is often necessary to attach a molecular spacer that facilitates mobility to terminal bioactive species.

Surface reactions were performed on polypropylene (PP) surfaces to retard the simultaneous growth of Staphylococcus aureus (S. aureus) and Pseudomonas putida (P. putida) bacteria. Microwave plasma reactions in the presence of maleic anhydride (MA) resulted in the formation of acid groups on the surface of PP. Such surfaces were further modified by conducting two parallel reactions: (1) poly(ethylene glycol) (PEG) was attached to COOH groups of the PP surface, followed by penicillin V (PEN) reactions to target S. aureus destruction and (2) diglycidyl PEG was attached, followed by gentamicin (GEN) reactions, to create antimicrobial surfaces targeted at P. putida . Simultaneous gram "+" and gram "-" resistance was obtained by varying the PEN/GEN ratios on such modified PP surfaces, thus providing the controllable degree of gram "+" and gram "-" antimicrobial strength. While spectroscopic analyses revealed chemical attachments of PEN and GEN, the effectiveness against proliferation of S. aureus (Gram +) and P. putida (Gram -) bacteria was determined using liquid culture tests. These studies show for the first time the formation of tunable antimicrobial polypropylene surfaces with controllable strength.

These studies report for the first time new thermal relaxations in stimuli-responsive solid-phase copolymers detected by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). When 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) and n-butyl acrylate (nBA) monomers were copolymerized into colloidal dispersions and allowed to coalesce to form solid continuous films, in addition to the glass-transition temperature (Tg), which follows the Fox equation for random copolymers, a new composition-sensitive endothermic stimuli-responsive transition (TSR) was observed. The TSR transition changes with the composition of the stimuli-responsive component of the copolymer, the temperature, and the rate of temperature change. On the basis of the experimental data, the following relationship was established: 1/TSR = w1/Tbinary + w2/T or 1/TSR = w1(1/Tbinary − 1/T) + 1/T, where TSR is the temperature of the stimuli-responsive transition, Tbinary is the temperature of the stimuli-responsive homopoly...

Reversible thermally induced arm release from a star polymer morphology was prepared which consists of furanic functional core and maleimide functional arm which are attached or detached via Diels–Alder (DA) reversible reactions. This approach allows the reversible bonding and debonding at 35–40 °C (DA) and 90–100 °C (retro-DA). The covalent reversibility of this process consists of 7 cycles of the DA and retro-DA reactions.

2-(N,N-Dimethylamino)ethyl methacrylate (DMAEMA) and n-butyl acrylate (nBA) monomers were copolymerized to form p(DMAEMA/nBA) colloidal particles that exhibit pH- and temperature-responsive behavior. Aqueous p(DMAEMA/nBA) colloidal dispersions exhibit second-order lower critical solution temperature (II-LCST) transition, referred to as stimuli-responsive temperature (TSR) for solid films, in the 27−37 °C range manifested by the particle size changes from 148 to 80 nm. Upon pH changes from 2 to 10, the particle size also changed from 205 to 139 nm. When p(DMAEMA/nBA) colloidal particles were allowed to coalesce which was facilitated by the presence of nBA component, the films retained their dual responsiveness and shrink in all the directions at T> TSR while expanding upon pH changes from basic to acidic. Thermodynamic molecular simulations combined with spectroscopic analysis showed that the temperature-responsive behavior results from the collapse of the (dimethylamino)ethyl groups and twisting/buckling ...

The broad spectrum antibiotic, ampicillin (AM), was reacted to expanded poly (tetrafluoroethylene) (ePTFE) surfaces and resulted in the formation of antimicrobial surfaces effective against gram-positive, Staphylococcus aureus, Bacillus thuringiensis, and Enterococcus faecalis, and gram-negative, Escherichia coli, Pseudomonas putida, and Salmonella enterica bacteria. These ePTFE surface modifications were accomplished by utilization of microwave maleic anhydride (MA) plasma reactions leading to the formation of acid groups, followed by amidation reactions of heterofunctional NH 2/COOH-terminated polyethylene glycol (PEG). The final step, the attachment of AM to the PEG spacer, was achieved by amidation reactions between COOH-terminated PEG and NH 2 groups of AM. This approach protects the COOH-AM functionality and diminishes the possibility of hydrolysis of the antimicrobial active portion of AM. These studies also show that approximately 90% of AM molecules are still covalently attached to PEG-MA-ePTFE surfaces after exposure to the bacteria solutions. Even after a 24 h period, the AM volume concentration changes only from 2.25 to 2.04 microg/m3, and depending upon the bacteria type, the bacteria suspensions containing AM-PEG-MA-ePTFE specimens retain 85-99% of their initial optical density.

These studies focus on the role of poly(vinyl alcohol) (pVOH) during colloidal synthesis of poly(methyl methacrylate/n-butyl acrylate) (pMMA/nBA) and its effect on particle coalescence. Using 2D photoacoustic FT-IR spectroscopy and internal reflection IR imaging, we showed that the presence of pVOH creates competing environments between the copolymer particle surfaces, aqueous phases, and dispersing agents which results in migration and self-induced stratification occurring during coalescence. pMMA/nBA/pVOH films stratify to form sodium dodecyl sulfate rich film-air interfaces, and the -SO3- moieties exhibit preferential parallel orientation with respect to the surface. At the same time, the bulk of the film is dominated by intramolecular hydrogen bonding between the pVOH phase and the copolymer matrix. This behavior is attributed to significant interactions between pVOH and pMMA/nBA, resulting in limited mobility of pVOH.

A new family of colloidal dispersions containing N-(dl)-(1-hydroxymethyl) propylmethacrylamide (dl-HMPMA) and n-butyl acrylate (nBA) monomers was developed which exhibits temperature-responsive behavior. Particle size analysis, along with UV−vis and 1H NMR spectroscopic measurements, showed that aqueous p(dl-HMPMA/nBA) particle dispersions display second-order lower critical solution temperature (II-LCST) in the 27−37 °C range at which the particle size decreases from 81 to 47 nm. When p(dl-HMPMA/nBA) colloidal particles were coalesced to form films, which is facilitated by the lower Tg nBA component that maintains an adequate free volume for temperature-responsive dl-HMPMA segments, coalesced films exhibited 3D directional responsiveness to temperature. While shrinkage occurs in the x−y plane directions (length and width, respectively), expansion in the z direction (thickness) above II-LCST is observed. Computer thermodynamics molecular simulations combined with the experimental data showed that conforma...

Because of unique properties of fluoropolymers, F-containing water dispersible colloidal dispersions continue to be of great interest and represent significant scientific challenges. These studies focus on the development and understanding of morphologies of F-containing colloidal particles synthesized in an aqueous phase in the presence of bioactive dispersing agents. When methyl methacrylate (MMA), n-butyl acrylate (n-BA), and heptadecafluorodecyl methacrylate (FMA) monomers are copolymerized in an aqueous phase, in the presence of phospholipids (PL), nonspherical particle morphologies are obtained. Their morphologies depend upon MMA/nBA ratios and lead to significantly different coalescence mechanisms and consequently surface properties. For higher MMA content, the particles are spherical, but at higher nBA contents, nonspherical morphologies are produced. This behavior is attributed to monomer starved conditions and the differences in reactivity ratios which forces copolymerization of FMA on the surfa...

Amphiphilic copolymer networks were prepared from hyperbranched fluoropolymer (HBFP*, Mn = 38 kDa, by atom transfer radical-self condensing vinyl copolymerization) and linear diamine-terminated poly(ethylene glycol) (DA-PEG, Mn = 1,630 Da). Model studies found that the crosslinking mechanism occurred at ambient temperature as a result of reaction between DA-PEG and the benzylic chlorides of HBFP*. These networks underwent covalent attachment to glass microscope slides derivatized with 3-aminopropyltriethoxysilane, whereupon gel percent studies at various weight percentages of DA-PEG to HBFP* found that curing could be achieved at lower temperatures and shortened time periods relative to the previously reported parent HBFP–PEG system. Thermogravimetric analysis revealed that the crosslinked materials gave no evident mass loss up to 250 °C. Differential scanning calorimetry of the complex amphiphilic networks showed a suppressed glass transition temperature, relative to that observed for neat HBFP*, and multiple melting DA-PEG endotherm(s) near 30 °C. The films possessed a topographically-complex surface with features that increased in tandem with an increase in the ratio of DA-PEG to HBFP*, as detected by atomic force microscopy and quantified by increased rms roughness values. Internal reflection infrared imaging revealed a heterogeneous surface composition and confirmed that the domain sizes increased as the weight percent of DA-PEG increased. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4782–4794, 2006

A new class of water-dispersible polyurethane pre-polymers bearing pendant unsaturation was synthesized and used with polyfunctional thiol crosslinkers to prepare uniform aqueous colloidal dispersions capable of forming crosslinked films upon UV exposure at 254 nm. This novel approach to prepare UV crosslinkable, water-based polyurethane polymers offers numerous advantages over other similar systems. Photocuring behavior of films from such thiol–ene polyurethane dispersions (TE-PUD) was monitored using ATR-FTIR spectroscopy by following consumption of thiol and ene functionalities as a function of UV exposure time. Dynamic mechanical analysis (DMA) revealed a decrease of the glass transition temperature ( T g ) with increasing thiol/ene ratios ranging from 0.5 to 1.1.

While waterborne two-component polyurethanes (WB 2K-PURs) offer an attractive approach toward the reduction of volatile organic compounds (VOC), a number of fundamental processes related to the colloidal stability and solution morphology of WB 2K-PUR reactive dispersions are not understood. These studies focus on mechanisms of inter-particle reactant aggregation in heterogeneous aqueous dispersions resulting from solution morphological changes of poly(ethylene glycol) modified water-dispersible polyisocyanates (WDPI) and water-reducible polyester polyol coreactants, as revealed by particle size measurements and in situ NMR T 2 studies. Based on the results of these experiments, a model of film formation is proposed which relates solution morphological features and chemical reactions. WDPI reactant droplets become hydrated over time, leading to formation of carbon dioxide, which dissolves in the aqueous continuum as carbonic acid and subsequently destabilizes anionically stabilized polyol droplets, resulting in their adsorption to WDPI droplet surfaces. The implications of polyol collapse, as they pertain to film formation, are discussed in the context of solution and film morphologies.

The development of a new family of colloidal dispersions that exhibit nonspherical shapes and are capable of forming stable polymeric dispersions and films is reported. Heptadecafluorodecyl methacrylate (FMA), heptadecafluorodecyl acrylate (FA), heptadecafluoro-1-decene (FD), heptafluorobutyl acrylate (FBA), and heptafluorobutyl methacrylate (FBMA) were copolymerized with methyl methacrylate (MMA) and n-butyl acrylate (nBA) monomers leading to the formation of stable colloidal dispersions that contain up to 8.5% (w/w) of F-containing polymer. Atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared (ATR FTIR) spectroscopy, and internal reflection infrared imaging (IRIRI) showed that the length of the perfluoroalkyl side chain in F-containing monomers is directly related to surface concentration levles in coalesced films. These studies also show that incorporation of each F-containing monomer generates surface properties with enhanced water repellency as well as significant de...

Methyl methacrylate (MMA) and n-butyl acrylate (nBA) were copolymerized into stable colloidal particles in the presence of micelle forming sodium dioctyl sulfosuccinate (SDOSS) and liposome forming 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) in aqueous media that serve as thermodynamically stable loci for lipophilic monomers and nanostructured templates. These studies show for the first time that hollow colloidal particles may coalesce to form polymeric films and the combination of SDOSS and DLPC dispersing agents provides a stimuli-responsive environment during film formation through which individual surface stabilizing components can be driven to the film-air (F-A) or film-substrate (F-S) interface. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) of p-MMA/nBA colloidal dispersions revealed preferential and enhanced mobility of SDOSS and DLPC lipid rafts to the F-A and F-S interfaces in response to thermal, ionic, and enzymatic stimuli.

A simple synthetic method for preparing stable colloidal dispersions that form polymeric films containing fluorinated acrylates is presented. The simultaneous presence of the dual tail anionic fluorosurfactant phosphoric acid bis(tridecafluorooctyl) ester ammonium salt (FSP) and sodium dodecyl sulfate (SDS) surfactants facilitates a suitable environment for the aqueous polymerization of methyl methacrylate/n-butyl acrylate/heptadecafluorodecyl methacrylate (MMA/nBA/FMA) colloidal particles. Polyermerization is achieved by a low-sheer monomer-starved emulsion polymerization process in which the FSP/SDS surfactant mixture significantly reduces the surface tension of the aqueous phase, thus facilitating mobility and subsequent polymerization of FMA along with MMA and nBA momomers. Using this approach, it is possible to obtain stable nonspherical MMA/nBA/FMA colloidal dispersions containing up to a 8.5% (w/w) copolymer content of FMA. These studies illustrate that the incorporation of FMA into MMA/nBA particl...

Microwave plasma reactions of imidazole, 2-methylimidazole, and 2-ethylimidazole on poly(dimethylsiloxane) (PDMS) surfaces resulted in the formation of species containing conjugated surface domains which can be utilized for further reactions. When imidazole and its derivatives were used, polymerization of imidazole and the formation of C=C and CN conjugated species occurred. However, the extent of reactions for each monomer depends on not only the reaction time but also the molecular structure. For methyl- and ethyl-substituted imidazole, more stable radical species are generated and sustain their excited state in the high-energy plasma environments. Specifically, dehydrogenated 2-methyl, 2-ethylimidazole radicals and (*)N=CR-NH(*) (R = -CH(3), -CH(2)CH(3)) species exhibit higher stability than dehydrogenated imidazole radicals and (*)N=CH-NH(*) species under plasma reaction conditions. Such prepared surfaces are capable of attaching antimicrobial drugs via the Pinner synthesis. These studies show that it is possible to react antimicrobial species such as chloramphenicol, and this promising approach offers numerous applications of microwave plasma reactions in biotechnology. Quantitative analysis of the depth of surface reactions was accomplished by using variable angle ATR FT-IR spectroscopy.

Hybrid acrylic/urethane colloidal dispersions were prepared by incorporation of a novel multifunctional urethane castor vinyl ether (UCVE) macromonomer derived from castor oil in acrylic latexes. Single-stage and two-stage semi-continuous emulsion polymerization processes were utilized to control placement of UCVE in colloidal dispersions with core/shell and spherical particle morphologies. While the single-stage process resulted in optically clear and chemically homogeneous films, the two-stage process led to heterogeneous film formation. Internal reflection infrared imaging (IRIRI) spectroscopic analysis of the film-air (F-A) interfaces revealed phase-separated urethane- and urea-rich domains ranging in size from approximately 4–40 μm. Based on these measurements, a model of film formation is proposed which incorporates the effect of exceedingly high shear conditions to achieve fine dispersions of UCVE. These experiments indicate that features of the single-stage process facilitate uniform dispersion of UCVE and efficient grafting between UCVE and the acrylic polymer matrix resulting in intimately mixed networks and homogeneous films.

These studies focus on the behavior of methalmethacrylate/n-butyl acrylate (MMA/n-BA) and methyl methacrylate/n-butyl acrylace/acrylic acid (MMA/nBA/AA) colloidal dispersions stabilized by sodium dodecyl sulfate (SDS). In MMA/n-BA, migration of SDS is apparent, but the presence of AA suppresses SDS mobility even at elevated temperatures. However, the addition of propylene glycol (PG) promotes SDS mobility. Internal reflection infrared imaging (IRIRI) data indicate that PG and SDS occupy the same areas, suggesting that both components reach the surface at the same time through the same transport mechanisms. As PG evaporates, SDS remains on the surface and likely forms crystalline phase. Using IRIRI imaging, with a spatial resolution of 1 μm, coalescence of MMA/nBA/AA was followed as a function of time. These studies show that the presence of AA in colloidal particles significantly alters not only film formation processes, but also SDS-particle interactions, thus minimizing mobility of SDS to the film−air (...

The surface morphology of coalesced latex films is a key parameter for understanding coalescence processes and physical and chemical properties of the resulting films. These studies focus on molecular aspects of colloidal film surfaces. Specifically, the distribution and orientation of a commonly used surfactant, sodium dodecyl sulfate (SDS), in films obtained from colloidal dispersions of poly(styrene/ethylhexyl acrylate/methacrylic acid) (Sty/EHA/MAA) and the effect of covalent and ionic entities incorporated into these films are examined. Apparently, the presence of covalently bonded species, such as diacetone acrylamide/adipic dihydrazide (DAAM/ADDH), or ionic species, such as Ca(OH)2/NH4OH, can effectively immobilize or mobilize SDS molecules during coalescence. Furthermore, molecular orientation of SDS is also influenced causing structural rearrangements near the film−air (F−A) interface. Upon coalescence at 25 °C, the −SO3-Na+ moieties take a preferentially parallel orientation, whereas at 60 °C th...

Fourier transform infrared spectroscopy was used to study the kinetics of noncatalyzed and catalyzed polyurethanes. These studies show that for noncatalyzed acrylic polyol–hexamethylene diisocyanate (HDI) trimer reactions, the reactions between OH and NCO of HDI exhibit second-order kinetics, with first-order kinetics with respect to NCO and OH. On the other hand, when dibutyltin dilaurate (DBTDL) is used as a catalyst in acrylic polyol–HDI trimer reactions, the reaction rate is first order with respect to NCO and 0.5 order in OH and DBTDL concentrations. A mechanism for the catalyzed acrylic polyol–HDI trimer crosslinking reactions is proposed and it appears that an equilibrium involving associations between OH and DBTDL exists, resulting in the formation of an active anion, which interacts with NCO to generate polyurethanes. To further verify this mechanism, the influence of acidity on the reaction rate constant was investigated. When the acidity of the system is increased, retardation of urethane formation occurs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2322–2329, 2002

This study focuses on the effect of sodium dioctylsulfosuccinate (SDOSS) and sodium dodecyl sulfate (SDS) surfactants on mobility and conformational behavior in styrene/n-butyl acrylate/methacrylic acid (Sty/n-BA/MAA) copolymer latex films. Because of similar hydrophilicity of SO3-Na+ groups but differences in hydrophobic tails, SDOSS and SDS are examined near the surface for coalesced Sty/n-BA/MAA latex films. These studies show that the presence of hydrophilic SO3-Na+ groups and hydrophobic entities represented by two C8H17 tails in SDOSS and one C12H25 hydrophobic group in SDS significantly affects the magnitude of surfactant−latex matrix interactions. Furthermore, not only the surfactant conformational behavior near the film−air interface is affected but also the magnitude of the interactions of hydrophilic SO3-Na+ groups in SDOSS with H2O and COOH groups of Sty/n-BA/MAA is substantially different from its SDS counterpart. This is demonstrated by the splitting of the S−O band when hydrophilic SDOSS gr...

In this study we utilized step-scan photoacoustic Fourier transform IR (SS-PA-FT-IR) spectroscopy to examine surface/interfacial properties of thermoplastic olefins (TPOs). This approach, combined with 2D FT-IR correlation analysis, allowed us to determine stratification processes in TPOs. These studies showed that the talc and polypropylene (PP) crystalline phase in TPO stratifies within the first 6–30 μm from the surface. Specifically, the PP crystalline phase exists at about 6.5 μm from the surface and its content diminishes at 7.1 μm, followed by reappearance around 11.3 μm, and becomes more prevalent upon approaching the bulk of TPO. Talc concentration levels show a similar pattern of change with depth across the interface, although absolute concentration levels differ from those of crystalline PP. These studies also demonstrated that SS-PA-FT-IR is a powerful tool in surface analysis, in particular for surface/interfacial analysis of multi-component polymeric systems.

Depth-profiling of talc/polypropylene (PP) compounded polymers with 5, 10, 15 and 20% talc weight percents were examined to delineate concentration effects on surface stratification. This was achieved by utilizing step-scan photoacoustic spectroscopy (S 2 PAS) phase analysis to discriminate molecular concentration changes for each species across a distance of 9 μm from the sample surface. From phase analysis results, it was determined that not only does talc lie 1–2 μm closer to the surface than PP, but a layering effect results from an increase in talc concentration. This layering effect results in depths 0–3 μm becoming saturated with talc molecules at lower talc concentrations, and layers 3–9 μm showing evidence of saturation at higher concentrations. At these higher concentrations and greater depths, it is postulated that PP is displaced by talc molecules giving rise to a boundary layer consisting mostly of talc.

Crosslinking reactions and stratification processes in polyurethane films were investigated using attenuated total reflectance (ATR) FTIR spectroscopy. The HDI trimer levels near the film–substrate (F–S) interface appear to increase at the early stages of reactions, and after reaching a maximum, decrease. This is attributed to solvent depletion and subsequent film shrinkage, thus causing local NCO concentration changes. At the later stages of crosslinking reactions, stratification of the 1,6-hexamethylene diisocyanate (HDI) trimer occurs, with higher concentration levels at shallower penetration depths from the F–S interface. At the same time, NCO-containing groups assume preferentially parallel orientation to the F–S interface. On the other hand, H-bonded carbonyl groups tend to orient themselves in a perpendicular direction. Quantitative analysis indicates that at extended reaction times the amount of H-bonded CO groups at shallower penetration depths increases and their orientation tends to be more random, which is correlated with migration toward the F–S interface. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2045–2054, 2001

Stratification of individual components in thermosetting coatings plays an important role during film formation and affects a number of macroscopic properties. This behavior is particularly pronounced for water-borne coatings, and therefore molecular level understanding of interactions in latexes and responsiveness of individual components during coalescence of water-borne polyurethanes are of particular interest. The presence of macromolecular arrangements and interactions among various components near the film–air (F–A) and the film–substrate (F–S) interfaces can be effectively monitored using attenuated total reflectance (ATR) and step-scan photoacoustic (SSPA) Fourier transform infrared (FT-IR) spectroscopy. Both approaches are capable of obtaining information from various surface depths and complement each other if one seeks molecular level information from 0 to 150 μm into the film. In this presentation combined ATR and PA information along with IR and/or Raman surface imaging will be presented to establish three-dimensional representation of polyurethane film formation and the effect of copolymer/polymer blend latexes on coalescence processes in Sty/ n -BA.

While molecular level interactions between sulfonate groups of sodium dioctylsulfosuccinate (SDOSS) and COOH groups in styrene/n-butyl acrylate/methacrylate acid (Sty/n-BA/MAA) copolymer particles have been the subject of our earlier studies, the main focus of this work is to establish how MAA groups affixed to polymer latex particle surfaces will affect SDOSS mobility in Sty/n-BA/MAA latex films. The ultimate objective is to develop a series of model systems simulating the degree of neutralization of polymer surfaces and how it may alter polymer contractions and release of entropically attached molecules to interfacial regions. These studies show that the release of SDOSS molecules from MAA containing Sty/n-BA particles is attributed to two factors: (1) entropic effect due to increased compatibility resulting from surfactant penetration into latex particle surfaces and (2) enhanced particle out-layer glass transition temperature (Tg). The SDOSS release is inhibited when surface neutralization levels are...

These studies focus on behavior of sodium dioctylsulfosuccinate (SDOSS) surfactant molecules in styrene/n-butyl acrylate/glycidyl methacrylate (Sty/nBA/GMA) and styrene/n-butyl acrylate/methacrylic acid (Sty/nBA/MAA) blended latexes during their film formation process. Using a combination of Fourier transform infrared (FT-IR) microanalysis and FT-Raman techniques, not only stratification of SDOSS surfactant molecules during film formation process can be assessed but also the effect of latex particle structures and cross-linking reactions during coalescence can be determined. For Sty/nBA/GMA and Sty/nBA/MAA blended copolymer latexes, SDOSS exhibit nonuniform distributions at the film air (F−A) interface. However, for core/shell Sty/nBA-GMA and Sty/nBA-MAA blended latexes, SDOSS is distributed uniformly near the F−A interface, and its concentration levels are lower as compared to copolymer latex blends. At elevated coalescence temperatures, SDOSS migration to the F−A interface is prohibited due to cross-lin...

These studies show that polystyrene/poly(n-butyl acrylate) (p-Sty/p-nBA) latex blend coalescence is inherently affected by latex composition, p-Sty particle size, and the temperature difference between coalescence (Tc) and glass transition (Tg) temperatures. Sodium dioctylsulfosuccinate (SDOSS) surfactant molecules are expelled to the film−air (F−A) interface when Tc > Tg of the p-Sty phase. Quantitative attenuated total reflectance Fourier transform infrared (ATR FT-IR) analysis shows that SDOSS−H2O concentration levels near the F−A interface diminish for larger p-Sty latex particle sizes and the magnitude of the SDOSS−COOH interactions near the F−A interface exhibits similar trends. Furthermore, the amount of SDOSS expelled to the F−A interface is directly proportional to the p-Sty phase surface area. These studies also show that SDOSS hydrophilic ends are preferentially parallel to the F−A interface, while hydrophobic ends are preferentially perpendicular.