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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.

Film formation of waterborne two-component polyurethanes is exceedingly complex due to the heterogeneous nature along with simultaneous progression of several parallel physicochemical processes which include water evaporation, cross-linking reactions, phase separation, and droplet coalescence, to name a few. While internal reflection infrared imaging (IRIRI) spectroscopy clearly facilitates analysis of chemical changes resulting from film formation, the complexity of processes leading to formation of specific surface/interfacial entities is a major experimental challenge. For this reason, we combined a spectrum of surface/interfacial analytical approaches including IRIRI, atomic force microscopy, and attenuated total reflectance Fourier transform infrared spectroscopy with Monte Carlo computer simulations to advance the limited knowledge of how temperature, stoichiometry, concentration levels, and reactivities of individual components affect the development of surface morphologies and compositional gradients across the film thickness. These studies show that in heterogeneous systems having both hydrophobic and hydrophilic components stratification of individual components to the film-air (F-A) interface is ultimately responsible for formation of rough surface topographies. These studies show that simultaneous stratification of hydrophobic components along with water evaporation to the F-A interface results in metastable interfacial layers, leading to surface dewetting. Subsequently, surface roughness is enhanced by higher concentrations of water in the cross-linking film.

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.

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 (...

Reversible addition−fragmentation chain transfer (RAFT) is a versatile, controlled free radical polymerization technique that operates via a degenerative transfer mechanism in which a thiocarbonylthio compound acts as a chain transfer agent. The subsequent reduction of the dithioester end groups to thiols allows the preparation of (co)polymer-modified gold surfaces. Herein we report the immobilization of poly(sodium 4-styrenesulfonate), poly((ar-vinylbenzyl) trimethylammonium chloride), poly(N,N-dimethylacrylamide), and poly(3-[2-(N-methylacrylamido)-ethyldimethyl ammonio]propane sulfonate-b-N,N-dimethylacrylamide) onto gold films. The presence of the immobilized (co)polymers was confirmed by atomic force microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, and surface contact angle measurements. The gold film modified with the block copolymer demonstrated stimuli-responsive behavior as evidenced by its water contact angle being similar to that of poly(N,N-dimethylacrylamide) ...

This report presents how combination of internal reflection (IR) and infrared imaging (IRI) can reach a surface spatial resolution at 1000 nm levels in the middle infrared range. As a result, vibrational spectra from these size areas can be recorded at high signal-to-noise levels. A spatial calibration of this method was performed by correlating IRIRI data with SEM micrographs and optical images of geometrically well-defined polymeric photoresists as well as Nylon fibers imbedded into a polyester matrix. The IRIRI approach has the potential of obtaining even better surface spatial resolution of vibrational spectra when internal reflection elements with greater refractive index ratios in the middle IR range become available.

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...

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...

Step-scan photoacoustic Fourier transformed infrared (FT-IR) spectroscopy, FT-IR microscopy, and Raman chemical imaging were utilized to examine molecular level degradation processes in epoxy (EP) and polyurethane (PUR) films. A combination of these techniques allowed us to determine a three-dimensional representation of degradation processes and showed that the extent of cross-linking in EP films varies as a function of depth from the surface. When exposed to 340 nm ultraviolet (UV) radiation and water vapor condensation, EP films degrade to form cracks on the surface, which are composed of primary amines and result from a chain scission of the C−N bonds in cross-linked bisphenol A EP films. PUR films exhibit the presence of two surface domains, which are composed of PUR- and polyurea (PUA)-rich regions. When exposed to 340 nm UV radiation and water vapor condensation, PUA is converted to PUR entities. Mechanisms leading to these processes are proposed and indicate that isocyanate and polyol reactions oc...

These studies show that maleic anhydride and carboxylic acid groups can be chemically bonded to poly(vinylidene fluoride) (PVDF) surfaces with the use of microwave plasma energy. Maleic anhydride reacts with the PVDF surface through a CC bond opening of the maleic anhydride ring, and its hydrolysis results in chemically attached carboxylic acid groups on the PVDF surface. The extent of the surface reactions can be monitored using attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectroscopy. These studies also show that maleic anhydride CO groups are preferentially parallel to the PVDF surface, and molecular mechanics force field calculations indicate that the most favorable angle between maleic anhydride and a polymer backbone is 25°. Quantitative spectroscopic analysis shows that before hydrolysis, volume concentrations of maleic anhydride vary from 1.32 × 10-5 to 7.94 × 10-5 mg/cm3 (surface concentrations from 1.8 × 10-9 to 6.67 × 10-9 mg/cm2), whereas the carboxylic acid content cha...

Although our recent studies revealed that under Ar microwave plasma conditions reactions of imidazole with poly(dimethylsiloxane) (PDMS) result in the formation of Si−CH2−imidazole species, the issue of the discharge gas effect on microwave plasma reactions remain unanswered. This study examines how these reactions in the presence of Ar, O2, and CO2 gases under microwave plasma conditions will affect surface reactions on PDMS in the presence of imidazole vapors. When Ar microwave plasma reaction conditions are employed, imidazole molecules react to the PDMS surface through hydrogen abstraction of the N−H bonds to form Si−CH2−imidazole and Si−CH2−CH3 linkages. When O2 microwave plasma reactions are conducted for 20 s or less discharge times, Si−O−imidazole and Si−O−CH3 species on the PDMS surface are formed. On the other hand, for discharge times above 20 s, the Si−O−CH3 linkages are converted to Si−O−CH2−imidazole entities as a result of hydrogen abstraction. The CO2 microwave plasma reactions in the pres...

These studies focus on the formation of multilayered thromboresistant thin films containing poly-(ethylenimine) (PEI), dextran sulfate (DS), and heparin (HP), deposited on poly(vinyl chloride) surfaces. Dipping and spin-coating are employed to deposit multilayers, and using attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectroscopy, the effects of pH, concentration of surface reacting species, and cross-linking conditions on the formation of multilayered structures are investigated. Quantitative ATR FT-IR analysis reveals that, when thin films are deposited by dipping, HP is immobilized to form covalent -CH 2 NH- linkages between PEI-NH 2 , and terminal HP-CHO groups. However, when spin-coating is utilized as an application method, HP takes a parallel orientation, and ionic complexes between PEI-NH 3 + (OH - ) and HP-SO 3 - (H 3 O + ) are formed. Quantitative analysis indicates that the surface concentration of individual layers is significantly lower for spin-coated layers.

Recently initiated studies concerning surface modifications of poly(dimethylsiloxanes) using microwave plasmons were extended to polyurethane (PU) surfaces. However, when the same experimental conditions used in the closed and open flow microwave plasma reactors were applied, no chemical bonding of imidazole molecules to PU surfaces was detected. In order to facilitate the imidazole−urethane surface reactions, PU specimens were immersed in an imidazole-containing methylene chloride solution and exposed to Ar microwave plasmons. This approach appears to be successful in creating chemically stable imidazole species attached to PU surfaces. Imidazole molecules are bonded to PU surfaces through the CN bond opening of imidazole, to create C−O−C surface bonds. Analysis of the imidazole−urethane linkages was accomplished using attenuated total reflectance Fourier transform infrared spectroscopy and revealed that the same surface structures on PU surfaces, but different concentration levels of imidazole at variou...

Our recent studies were concerned with the microwave plasma reactions of imidazole molecules to cross-linked poly(dimethylsiloxane) (PDMS) surfaces. However, the issue of the PDMS surface sites responsible for imidazole bonding reactions remained open. In this study, attenuated total reflectance (ATR) Fourier transform infrared (FT-IR) spectroscopy will be used to assess the origin of species responsible for the PDMS reactions with imidazole. Analyses of spectroscopic data indicate that the primary reactive sites on the PDMS surfaces are Si−CH2• radicals, which are formed through the hydrogen abstraction of the Si−CH3 groups. The Si−CH2• radicals react with the imidazole CHCHNCHN• radicals, resulting from hydrogen abstraction of the N−H bonds, to form Si−CH2−imidazole surface entities. Reaction mechanisms responsible for imidazole−PDMS reactions in microwave plasma are proposed.

Although there are various forms of energy available for conducting surface and interfacial reactions, microwave energy generated plasmas appears to be an effective source for reacting monomeric molecules to elastomeric surfaces. In this study, closed and open flow microwave plasma reactors were developed and utilized to react imidazole molecules to cross-linked polydimethylsiloxanes (PDMS) surfaces. Using closed reactor, imidazole molecules are chemically bonded on the PDMS surface through hydrogen abstraction of the N-H bonds of imidazole. Their orientation, as determined by polarized ATR FT-IR spectroscopy, appears to be preferentially parallel to the PDMS surface. The amount of imidazole reacted to the PDMS surface increases at discharge pressures not exceeding 53.3 Pa, and discharge times not exceeding 20 s. Extended discharge times, however, are destructive to chemically attached imidazole molecules to PDMS. In the open flow reactor, imidazole molecules are reacted to the PDMS surface by ring opening of the imidazole entity to form C=N surface species. Both reactivity and the extent of the ring opening reactions can be controlled by the plasma reaction parameters, discharge pressure, and time. The presence of silica microdomains on PDMS surface inhibits imidazole reactions to PDMS.

Using nano- and microsize extrusion, a simple synthetic procedure of preparing hollow monodispersed colloidal particles dispersed in an aqueous phase was developed. Hydrophobic styrene monomer containing 2-hydroxy-2-methyl propiophenone photoinitiator was forced into desired diameter membrane channels and stabilized by the hydrophobic regions of a liposome obtained from 1,2-dilauroyl-phosphocholine phospholipid in an aqueous phase. Such moieties exposed to 254-nm UV radiation polymerize monomers in the hydrophobic zone of the liposome, thus resulting in reinforced hollow vesicles. The size of such particles is controlled by the size of the membrane channels in the extruder and may vary from a few nanometers to micrometers, thus allowing the synthesis of monodisperse hollow colloidal spheres.