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Polymeric colloids have shown potential as "building blocks" in applications ranging from formulations of Pickering emulsions and drug delivery systems to advanced materials, including colloidal crystals and composites. However, for applications requiring tunable properties of charged colloids, obstacles in fabrication can arise through limitations in process scalability and chemical versatility. In this work, the capabilities of flash nanoprecipitation (FNP), a scalable nanoparticle (NP) fabrication technology, are expanded to produce charged polystyrene colloids using sulfonated polystyrene ionomers as a new class of NP stabilizers. Through experimental exploration of formulation parameters, increases in the ionomer content are shown to reduce the particle size, mitigating a significant trade-off between the final particle size and inlet concentration; thus, expanding the processable material throughput of FNP. Further, the degree of sulfonation is found to impact stabilization with optimal performance achieved by selecting ionomers with intermediate (2.45-5.2 mol %) sulfonation. Simulations of single ionomer chains and their arrangement in multicomponent NPs provide molecular insights into the assembly and structure of NPs wherein the partitioning of ionomers to the particle surface depends on the polymer molecular weight and degree of sulfonation. By combining the insights from simulations with diffusion-limited growth kinetics and parametric fits to experimental data, a simple design formulation relation is proposed and validated. This work highlights the potential of ionomer-based stabilizers for controllably producing charged NP dispersions in a scalable manner.

Wet processing of graphene sheets is a potentially interesting route for economically viable creation of graphene based composites. In the present work flow dichroism and small angle light scattering are used to investigate the dispersion of functionalized graphene sheets in suspension and their response to shear flow. In line with expectations from scaling theory at rest, the functionalized graphene sheets are present as Brownian, flat sheets, and there is no evidence of significant crumpling. More surprisingly, we find that the rate dependent orientation of these molecularly thin sheets can be described by numerical predictions for hard spheroidal sheets making quantitative predictions of the flow induced orientation possible. Further comparing the flow induced orientation of thick gold decahedra with the thin graphene sheets shows that, except for effects of polydispersity, the flow induced orientation is predicted well quantitatively. Adequate prediction of the effects of flow on orientation of graphene sheets makes it possible to design wet processed graphene based composite materials. The authors thank Luiz Lis-Marzan, Jorge Perez-Juste, and Isabel Pastoriza-Santos for providing oblate gold spheroids. J.V. acknowledges the Swiss National Science Foundation (project number 200021-157147), and G.N. acknowledges funding from the NSERC (grant number RGPIN-2017-03783). The authors thank the reviewers for insightful comments on the article, as these comments led us to improve it.

Although many theories exist to understand the transport of surfactants to and along interfaces under flow, few techniques are available to directly monitor surfactant dynamics at interfaces. Due to the broad use of surfactants, from oil spill remediation to healthcare and household products, a better means of assessing surfactant dynamics would be widely applicable. Here, we describe and demonstrate the use of fluorescent surfactant-dyes as a means of dynamic visualization of surfactant transport and have synthesized Nile Red/polyethylene glycol (NR-PEG) derivatives for this purpose. These NR-PEG surfactant-dyes fluoresce differently at oil-water interfaces than in bulk aqueous solution, allowing for the selective monitoring of bound and free surfactant using confocal microscopy. We have visualized the transport of surfactants to and along interfaces of droplets in a pipe flow and at the interfaces of liquid-infused surfaces undergoing shear-driven drainage. Imaging surfactant adsorption to interfaces at these time scales will allow for the development of improved dispersant systems for applications such as oil spill remediation and can also be used in understanding other fundamental transport phenomena involving dispersants.

In an effort to incorporate increasingly higher levels of functionality into soft nanoparticles, heterogeneously structured particles stand out as a simple means to enhance functionality by tailoring only particle architecture. Various means exist for the fabrication of particles with specific structural configurations; however, the tunability of particle morphology is still a challenging and often laborious task, especially in self-assembled systems where a single equilibrium configuration dominates. Improved strategies for multipatch particle assembly are therefore needed to allow for the tailoring of particle structure via a single, continuous assembly route. One means of accomplishing this is through kinetic trapping of particle morphologies along the path to the final equilibrium configuration in precipitation-induced, phase-separating polymer blends. Here, we demonstrate this capability by using rapid nanoprecipitation to control the overall size, composition, and patch distribution of soft colloids. In particular, we illustrate that polymer feed concentration, blend ratio, and polymer molecular weight can all serve as functional handles with which to consistently alter particle patch distributions in a self-assembling homopolymer system without redesigning the starting materials. We furthermore delineate the role of polymer vitrification in the determination of particle structure.

We have developed pH-responsive, multifunctional nanoparticles based on encapsulation of an antioxidant, tannic acid (TA), using flash nanoprecipitation, a polymer directed self-assembly method. Formation of insoluble coordination complexes of tannic acid and iron during mixing drives nanoparticle assembly. Tuning the core material to polymer ratio, the size of the nanoparticles can be readily tuned between 50 and 265 nm. The resulting nanoparticle is pH-responsive, i.e., stable at pH 7.4 and soluble under acidic conditions due to the nature of the coordination complex. Further, the coordination complex can be coprecipitated with other hydrophobic materials such as therapeutics or imaging agents. For example, coprecipitation with a hydrophobic fluorescent dye creates fluorescent nanoparticles. In vitro, the nanoparticles have low cytotoxicity and show antioxidant activity. Therefore, these particles may facilitate intracellular delivery of antioxidants.

Biocompatible nanocomposite hydrogels (NC gels) consisting of poly(acrylic acid) (PAA) and nanosized clay (Laponite) were successfully synthesized by in situ free-radical polymerization of acrylic acid (AA) in aqueous solutions of Laponite. The obtained NC gels were uniform and transparent. Their viscosity, storage modulus G', and loss modulus G″ increased significantly upon increasing the content of Laponite and the dose of AA, while exhibiting a maximum with increasing the neutralization degree of AA. They showed tunable adhesion by changing the dose of Laponite and monomer as well as the neutralization degree of AA, as determined by 180° peel strength measurement. The maximal adhesion was shown when reaching a balance between cohesion and fluidity. A homemade Johnson-Kendall-Roberts (JKR) instrument was employed to study the surface adhesion behavior of the NC gels. The combination of peel strength, rheology, and JKR measurements offers the opportunity of insight into the mechanism of adhesion of hydrogels. The NC gels with tunable adhesion should be ideal candidates for dental adhesive, wound dressing, and tissue engineering.

There is considerable current interest in developing methods to integrate nanoparticles into optical, electronic, and biological systems due to their unique size-dependent properties and controllable shape. We report herein a versatile new approach for covalent immobilization of nanoparticles onto substrates modified with photoactive, phthalimide-functional, self-assembled monolayers. Upon illumination with UV radiation, the phthalimide group abstracts a hydrogen atom from a neighboring organic molecule, leading to radical-based photografting reactions. The approach is potentially "universal" since virtually any polymeric or organic-inorganic hybrid nanoparticle can be covalently immobilized in this fashion. Because grafting is confined to illuminated regions that undergo photoexcitation, masking provides a simple and direct method for nanoparticle patterning. To illustrate the technique, nanoparticles formed from diblock copolymers of poly(styrene-b-polyethylene oxide) and laden with Hostasol Red dye are photografted and patterned onto glass and silicon substrates modified with photoactive phthalimide-silane self-assembled monolayers. Atomic force microscopy and X-ray photoelectron spectroscopy are applied to characterize the grafted nanoparticle films while confocal fluorescence microscopy is used to image patterned nanoparticle deposition.

Flow can change the rate at which solutes adsorb on surfaces by changing mass transfer to the surface, but moreover, flow can induce changes in the conformation of macromolecules in solution by providing sufficient stresses to perturb the segmental distribution function. However, there are few studies where the effect of flow on macromolecules has been shown to alter the structure of macromolecules adsorbed on surfaces. We have studied how the local energy dissipation alters the adsorption of gelatin onto polystyrene nanoparticles ( r = 85 nm). The change in the nature of the adsorbed layer is manifest in the change in the ability of the nanoparticles to resist aggregation. Circular dichroism spectroscopy was used to assess conformational changes in gelatin, and dynamic light scattering was used to assess the colloid stability. Experiments were conducted in a vortex jet mixer where energy density and mixing times have been quantified; mixing of the gelatin and unstable nanoparticles occurs on the order of milliseconds. The adsorption of the gelatin provides steric stabilization to the nanoparticles. We found that the stability of the gelatin-adsorbed nanoparticles increased with increasing mixing velocities: when the mixing velocities were changed from 0.9 to 550 m/s, the radius of the nanoclusters (aggregates) formed 12 h after the mixing decreased from 2620 to 600 nm. Increasing temperature also gave rise to similar trends in the stability behavior with increasing temperature, leading to increasing colloid stability. Linear flow birefringence studies also suggested that the velocity fields in the mixer are sufficiently strong to produce conformational changes in the gelatin. These results suggest that the energy dissipation produced by mixing can activate conformational changes in gelatin to alter its adsorption on the surfaces of nanoparticles. Understanding how such conformational changes in gelatin can be driven by local fluid mechanics and how these changes are related to the adsorption behavior of gelatin is very important both industrially and scientifically.

A systematic study of the host−guest complexation by α-, β-, and γ-cyclodextrin (CD) in either the free state or as substituents of poly(acrylic acid) (PAA) with the hydrophobic n-octadecyl groups,...

Surface rheology of irreversibly bound hydrophobically modified poly(ethylene glycol) (PEG) polymers (HMPEG) on a dipalmitoylphosphatidylcholine (DPPC) monolayer is investigated to determine attributes that may contribute to immune recognition. Previously, three comb-graft polymers (HMPEG136-DP3, HMPEG273-DP2.5, and HMPEG273-DP5) adsorbed on liposomes were examined for their strength of adsorption and protection from complement binding. The data supported an optimal ratio between the hydrophilicity of the PEG polymer and the number of hydrophobic anchors. The HMPEG polymers have different polymer brush thicknesses (4.2-5.9 nm) and levels of cooperativity (2.5-5 hydrophobes). The results indicate that an increased viscous force (above 0.25 mN s/m) at the surface may enable the polymers to shield liposomes from protein interactions. Similar rheological behavior is shown for all polymer architectures at low polymer surface coverage (0.5 mg/m2, in the mushroom regime), whereas at high surface coverage (0.5 mg/m2, in the brush regime), we observe a structural dependence of the surface viscous forces at 40 mN/m. This threshold correlates with a 92% decrease in complement protein binding for liposomes coated with 1 mg/m2 HMPEG273-DP5. This may suggest that surface viscous forces play a role in reducing complement protein binding.

We describe the preparation and characterization of hybrid block copolymer nanoparticles (NPs) for use as multimodal carriers for drugs and imaging agents. Stable, water-soluble, biocompatible poly(ethylene glycol)-block-poly(epsilon-caprolactone) NPs simultaneously co-encapsulating hydrophobic organic actives (beta-carotene) and inorganic imaging nanostructures (Au) are prepared using the flash nanoprecipitation process in a multi-inlet vortex mixer. These composite nanoparticles (CNPs) are produced with tunable sizes between 75 nm and 275 nm, narrow particle size distributions, high encapsulation efficiencies, specified component compositions, and long-term stability. The process is tunable and flexible because it relies on the control of mixing and aggregation timescales. It is anticipated that the technique can be applied to a variety of hydrophobic active compounds, fluorescent dyes, and inorganic nanostructures, yielding CNPs for combined therapy and multimodal imaging applications.

Reactive impingement mixing was employed to produce polymer-protected nanoparticles. Amphiphilic block copolymer was formed in situ by reactive coupling of hydrophobic and hydrophilic blocks. Simultaneously, a hydrophobic compound and the copolymer coprecipitated to form nanoparticles in the range of 100 nm. Specifically, beta-carotene was stabilized by the amphiphilic diblock copolymer, formed from the reaction of an amino-terminated hydrophilic block, poly(ethylene glycol) (PEG-NH2), with an acid chloride-terminated hydrophobic block, either poly(epsilon-caprolactone) (PCL-COCl) or polystyrene (PS-COCl). Spherical particles were observed by scanning and cryogenic transmission electron microscopy. Process conditions, including feed concentration of beta-carotene and feed concentrations of polymeric stabilizers, had little or no effect on average particle sizes over the range studied. Further, for Reynolds numbers greater than 500 the feed flow rates also had no effect. The effect of glass transition temperature (Tg) of the hydrophobic polymer on morphology and particle formation mechanism is discussed.

The linear viscoelastic response of erucyl bis(hydroxyethyl) methylammonium chloride with added KCl has been studied as a function of temperature and nonpolar solvent addition. The plateau modulus is independent of temperature from 25 to 40 degrees C, in contrast to previous studies with salicylate counterions that showed a plateau modulus increasing with temperature over this range. The average micelle length, L, predicted by the model of Cates, depends experimentally on Escis/kBT, where Escis is the scission energy of the chain and kBT is the Boltzmann constant times the absolute temperature. With ethanol addition, the calculated average contour length, L, decreases by a factor of 4 as ethanol concentration varies from 0 to 1.3 M. This corresponds to an apparent energy for scission, Escis, decrease from 81 +/- 8 to 74 +/- 7 kJ/mol. On the other hand, only 80 mM of hexane is required to cause a decrease in Escis to the same level, and for hexane addition levels above 70 mM a disruption in the plateau modulus indicates the disruption of the rodlike structure. The correspondence between the effect of temperature and the effect of solvent addition allows the development of "solvent/temperature" superposition rules to predict the rheology of these viscoelastic fluids at elevated temperatures.

Interactions between hydrophobically modified polymers (hm-polymers) and surfactants were investigated by steady-state fluorescence as well as rheological experiments. Hydrophobically modified hydroxyethylcellulose (hmHEC) with C16 hydrophobe grafts of 0.9% mole along with tetradecyltrimethylammonium bromide and cetyltrimethylammonium bromide were studied. The presence of C16HEC induced the aggregation of surfactant micelles in aqueous solution at concentrations about one-half times lower than the critical micelle concentration. As surfactant is added, the viscosity of hm-polymer solution first increases due to the bridging of hydrophobe clusters by surfactant micelles to form mixed micelles and later decreases due to the masking of hydrophobes individually by excess micelles. Fluorescence quenching experiments showed that the number of hydrophobes (NH) in a mixed micelle decreases steadily with increasing surfactant concentration due to hydrophobe dilution by the surfactant. NH declines from greater than...

We characterize the effect of adsorbed hydrophobically modified polymers (hm-polymers) on the dynamics of surfactant bilayers by small-angle neutron scattering and neutron spin-echo spectroscopy. Two kinds of hm-polymers, (a) hydrophobically modified poly(acrylate) with tetradecyl (C-14) sidegroups randomly grafted to the poly(acrylate) backbone and (b) poly(PEG(6k)-lysine-stearylamide) with equally spaced hydrophobes, are added to bilayers of penta(ethylene glycol) dodecyl ether (C12E5) and hexanol. Both bare and polymer-doped membranes exhibit a stretched exponential relaxation in the form of S((q) over bar ,t) 2; S((q) over bar) exp[-(Gamma(q)t)(2/3)], where S(q) is the static structure factor and Gamma(q) is the relaxation rate. The relaxation rate depends subtly on the surface coverage of polymer. At high surface coverage, polymer slows down the relaxation by 20%, whereas at low surface coverage, polymer enhances the rate relative to that of the bare membranes. Hindered flow of solvent through the adsorbed polymer layer at high coverage appears to explain the retardation. The faster dynamics at low polymer coverage may be due to stiffening of the membrane or lateral diffusion of the dilute adsorbed polymer chains.

The ability of three novel polymers to protect phosphatidylethanolamine/phosphatidylserine (1:1) vesicles against calcium-induced destabilization (dye leakage) has been investigated. The polymers are a telechelic, hydrophobically terminated poly(ethylene glycol) (PEG), a polymer of the macromonomer PEG8000−lysine-stearylamide, and a hydrophobically modified poly(acrylic acid). These polymers are predominantly hydrophilic but have multiple hydrophobic moieties which serve to anchor them in the lipid bilayers. Like singly anchored PEG, the two PEG-based polymers were able to provide effective stabilization at concentrations sufficient to produce a polymer “brush” on the liposome surface. Interestingly, the poly(acrylic acid) polymer did not provide full stabilization even at concentrations that should have produced brush coverage, possibly owing to a more expanded polymer conformation. The potential advantages of stabilization with polymers having multiple “sticky feet” are discussed.

We study the effect of hydrophobically modified polymers (hm-polymers) on the phase behavior and membrane elastic properties of the lyotropic lamellar (Lα) phase of the nonionic surfactant penta(ethylene glycol) dodecyl ether (C12E5). The hm-polymer is a model comb-graft polymer with monodisperse PEG blocks (loops) of 6, 12, or 35 kg/mol connecting C18 stearylamide hydrophobes. The polymer is of interest because both its loops and hydrophobes are biocompatible. The membrane properties are extracted from the small-angle neutron scattering data based on the model of Nallet et al. The monophasic Lα region exists over a narrower membrane volume fraction range but to a higher polymer concentration for hmPEGs with larger PEG spacers. The rigidity of the membranes increases by 40% with decreasing PEG spacer size from 12 to 6 kg/mol or increasing polymer concentration. For hmPEG polymers with 2−3 loops, the effect of finite chain lengths plays a role on the phase behavior and membrane properties.

Thin, supported decane films stabilized with comb−graft copolymers were studied as models of polymeric surfactant stabilized water-in-oil emulsions. The stabilizing polymeric surfactant (“polysoap”...

Small-angle neutron scattering (SANS) and rheometry were used to investigate the supramolecular structure formed by a poly(oxyethylene−oxypropylene−oxyethylene) (PEO100PPO65PEO100, Pluronic F127) copolymer in aqueous solution over a temperature range of 10−75 °C and a concentration range of 10−20 wt %. At copolymer concentrations of less than 12.5% the solutions are Newtonian fluids. Gels with an ordered structure (cubic packing of spherical micelles) are observed over a well-defined temperature window when the copolymer concentrations are greater than 17 wt %. The SANS results show that the aggregation number of the micelles is independent of temperature and concentration. Low-yield stresses, very high zero shear viscosities (∼106 P), and shear thinning are the major rheological characteristics of the gels. Near, but outside, the gel phase boundary the solutions are non-Newtonian (shear thinning). However, SANS shows these solutions contain domains having the same structure as that in the gel phase. The ...