@article{kopyshev_galvin_patil_genzer_lomadze_feldmann_zakrevski_santer_2016, title={Light-Induced Reversible Change of Roughness and Thickness of Photosensitive Polymer Brushes}, volume={8}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.6b06881}, abstractNote={We investigate light-induced changes in thickness and roughness of photosensitive polymer brushes containing azobenzene cationic surfactants by atomic force microscopy (AFM) in real time during light irradiation. Because the cis-state of azobenzene unit requires more free volume than its trans counterpart, the UV light-induced expansion of polymer thin films associated with the trans-to-cis isomerism of azobenzene groups is expected to occur. This phenomenon is well documented in physisorbed polymer films containing azobenzene groups. In contrast, photosensitive polymer brushes show a decrease in thickness under UV irradiation. We have found that the azobenzene surfactants in their trans-state form aggregates within the brush. Under irradiation, the surfactants undergo photoisomerization to the cis-state, which is more hydrophilic. As a consequence, the aggregates within the brush are disrupted, and the polymer brush contracts. When subsequently irradiated with blue light the polymer brush thickness returns back to its initial value. This behavior is related to isomerization of the surfactant to the more hydrophobic trans-state and subsequent formation of surfactant aggregates within the polymer brush. The photomechanical function of the dry polymer brush, i.e., contraction and expansion, was found to be reversible with repeated irradiation cycles and requires only a few seconds for switching. In addition to the thickness change, the roughness of the brush also changes reversibly between a few Angstroms (blue light) and several nanometers (UV light). Photosensitive polymer brushes represent smart films with light responsive thickness and roughness that could be used for generating dynamic fluctuating surfaces, the function of which can be turned on and off in a controllable manner on a nanometer length scale.}, number={29}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Kopyshev, Alexey and Galvin, Casey J. and Patil, Rohan R. and Genzer, Jan and Lomadze, Nino and Feldmann, David and Zakrevski, Juri and Santer, Svetlana}, year={2016}, month={Jul}, pages={19175–19184} }
 @article{kopyshev_galvin_genzer_lomadze_santer_2016, title={Polymer brushes modified by photosensitive azobenzene containing polyamines}, volume={98}, ISSN={["1873-2291"]}, DOI={10.1016/j.polymer.2016.03.050}, abstractNote={This paper describes a strategy for preparing photosensitive polymeric grafts on flat solid surfaces by loading diblock-copolymer or homopolymer brushes with cationic azobenzene-containing surfactants. In contrast to previous work, we utilize photosensitive surfactants that bear positively-charged polyamine head groups whose charge varies between 1+ and 3+. Poly(methylmethacrylate-b-methacrylic acid) (PMMA-b-PMAA) brushes were prepared by employing atom transfer radical polymerization, where the bottom poly(methyl methacrylate) block was grown first followed by the synthesis of t-butyl methacrylate block that after de-protection yielded poly(methacrylic acid). We used PMMA-b-PMAA brushes with constant grafting density and length of the PMMA block, and three different lengths of the PMAA block. The azobenzene-based surfactants attached only to the PMAA block. The degree of binding (i.e., the number of surfactant molecules per binding site on the brush backbone) of the surfactants to the brush depends strongly on the valence of the surfactant head-group; within the brushes the concentration of the surfactant carrying unit charge is larger than that of multivalent surfactants. We detect pronounced response of the brush topography on irradiation with UV interference pattern even at very low degree of binding (as small as 0.08) of multi-valence surfactant. Areas on the sample that receive the highest UV dose exhibit chain scission. By removing the ruptured chains from the substrate via good solvent, one uncovers a surface topographical relief grating, whose spatial arrangement follows the intensity distribution of the UV light on the sample during irradiation. Due to strong coupling of the multi-valence surfactants to the polymer brush, it was possible in some cases to completely remove the polyelectrolyte block from the PMMA layer. The application of multi-valence azobenzene surfactants for triggering brush photosensitive has important advantage over usage of surfactant with unit charge because relative to single-valence surfactants much lower concentrations of the multivalent surfactant are needed to achieve comparable response upon UV irradiation.}, journal={POLYMER}, author={Kopyshev, Alexey and Galvin, Casey J. and Genzer, Jan and Lomadze, Nino and Santer, Svetlana}, year={2016}, month={Aug}, pages={421–428} }
 @article{galvin_genzer_2016, title={Swelling of Hydrophilic Polymer Brushes by Water and Alcohol Vapors}, volume={49}, ISSN={["1520-5835"]}, DOI={10.1021/acs.macromol.6b00111}, abstractNote={We examine the effect of end-tethering, grafting density (σ), chemistry of polymer side chain, and solvent type on the vapor swelling of hydrophilic polymer brushes. Using a library of samples derived by postpolymerization modification of a poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brush, we determine the extent of vapor swelling and solvent uptake at different vapor pressures of water, methanol, and ethanol using spectroscopic ellipsometry. We compare the results from neat PDMAEMA and PDMAEMA quaternized by methyl iodide with chemically analogous samples prepared by spincasting bulk PDMAEMA. We find that brush samples swell to greater extents than spuncast samples, indicating a role for end-tethering in the vapor uptake process. Furthermore, vapor swelling of polymer brushes depends strongly on both polymer and solvent chemistry. We demonstrate that the extent to which σ affects vapor sorption inside the brush depends on polymer side chain chemistry, indicating an interdependence of the observe...}, number={11}, journal={MACROMOLECULES}, author={Galvin, Casey J. and Genzer, Jan}, year={2016}, month={Jun}, pages={4316–4329} }
 @article{galvin_bain_henke_genzer_2015, title={Instability of surface-grafted weak polyacid brushes on flat substrates}, volume={48}, number={16}, journal={Macromolecules}, author={Galvin, C. J. and Bain, E. D. and Henke, A. and Genzer, J.}, year={2015}, pages={5677–5687} }
 @article{gurarslan_hardrict_roy_galvin_hill_gracz_sumerlin_genzer_tonelli_2015, title={Beyond Microstructures: Using the Kerr Effect to Characterize the Macrostructures of Synthetic Polymers}, volume={53}, ISSN={["1099-0488"]}, DOI={10.1002/polb.23598}, abstractNote={ABSTRACTThe macrostructures of synthetic polymers are essentially the complete molecular chain architectures, including the types and amounts of constituent short‐range microstructures, such as the regio‐ and stereosequences of the inserted monomers, the amounts and sequences of monomers found in co‐, ter‐, and tetra‐polymers, branching, inadvertent, and otherwise, etc. Currently, the best method for characterizing polymer microstructures uses high field, high resolution 13C‐nuclear magnetic resonance (NMR) spectroscopy observed in solution. However, even 13C‐NMR is incapable of determining the locations or positions of resident polymer microstructures, which are required to elucidate their complete macrostructures. The sequences of amino acid residues in proteins, or their primary structures, cannot be characterized by NMR or other short‐range spectroscopic methods, but only by decoding the DNA used in their syntheses or, if available, X‐ray analysis of their single crystals. Similarly, there are currently no experimental means to determine the sequences or locations of constituent microstructures along the chains of synthetic macromolecules. Thus, we are presently unable to determine their macrostructures. As protein tertiary and quaternary structures and their resulting ultimate functions are determined by their primary sequence of amino acids, so too are the behaviors and properties of synthetic polymers critically dependent on their macrostructures. We seek to raise the consciousness of both synthetic and physical polymer scientists and engineers to the importance of characterizing polymer macrostructures when attempting to develop structure–property relations. To help achieve this task, we suggest using the electrical birefringence or Kerr effects observed in their dilute solutions. The molar Kerr constants of polymer solutes contributing to the birefringence of their solutions, under the application of a strong electric field, are highly sensitive to both the types and locations of their constituent microstructures. As a consequence, we may begin to characterize the macrostructures of synthetic polymers by means of the Kerr effect. To simplify implementation of the Kerr effect to characterize polymer macrostructures, we suggest that NMR first be used to determine the types and amounts of constituent microstructures present. Subsequent comparison of observed Kerr effects with those predicted for different microstructural locations along the polymer chains can then be used to identify the most likely macrostructures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 155–166}, number={3}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Gurarslan, Rana and Hardrict, Shauntrece and Roy, Debashish and Galvin, Casey and Hill, Megan R. and Gracz, Hanna and Sumerlin, Brent S. and Genzer, Jan and Tonelli, Alan}, year={2015}, month={Feb}, pages={155–166} }
 @article{galvin_dimitriou_satija_genzer_2014, title={Swelling of Polyelectrolyte and Polyzwitterion Brushes by Humid Vapors}, volume={136}, ISSN={["1520-5126"]}, DOI={10.1021/ja5065334}, abstractNote={Swelling behavior of polyelectrolyte and polyzwitterion brushes derived from poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) in water vapor is investigated using a combination of neutron and X-ray reflectivity and spectroscopic ellipsometry over a wide range of relative humidity (RH) levels. The extent of swelling depends strongly on the nature of the side-chain chemistry. For parent PDMAEMA, there is an apparent enrichment of water vapor at the polymer/air interface. Despite extensive swelling at high humidity level, no evidence of charge repulsion is found in weak or strong polyelectrolyte brushes. Polyzwitterionic brushes swell to a greater extent than the quaternized brushes studied. However, for RH levels beyond 70%, the polyzwitterionic brushes take up less water molecules, leading to a decline in water volume fraction from the maximum of ~0.30 down to ~0.10. Using a gradient in polymer chain grafting density (σ), we provide evidence that this behavior stems from the formation of inter- and intramolecular zwitterionic complexes.}, number={36}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Galvin, Casey J. and Dimitriou, Michael D. and Satija, Sushil K. and Genzer, Jan}, year={2014}, month={Sep}, pages={12737–12745} }
 @article{hardrict_gurarslan_galvin_gracz_roy_sumerlin_genzer_tonelli_2013, title={Characterizing polymer macrostructures by identifying and locating microstructures along their chains with the kerr effect}, volume={51}, ISSN={["0887-6266"]}, DOI={10.1002/polb.23248}, abstractNote={AbstractIn this brief report, we demonstrate that Kerr effect measurements, which determine the excess birefringence contributed by polymer solutes in dilute solutions observed under a strong electric field, are highly sensitive to and capable of determining their microstructures, as well as their locations along the macromolecular backbone. Specifically, using atactic triblock copolymers with the same overall composition of styrene (S) and p‐bromostyrene (pBrS) units, but with two different block arrangements, that is, pBrS90‐b‐S120‐b‐pBrS90 (I) and S60‐b‐pBrS180‐b‐S60 (II), which are indistinguishable by NMR, we detected a dramatic difference in their molar Kerr constants (mK), in agreement with those previously estimated. Although similar in magnitude, their Kerr constants differ in sign, with mK(II) positive and mK(I) negative. In addition, S/pBrS random and gradient copolymers synthesized by reversible addition‐fragmentation chain‐transfer (RAFT) polymerization exhibit a heretofore unexpected enhanced enchainment of racemic (r) pBrS‐pBrS diads. Comparison of their observed and calculated mKs suggests that the gradient S/pBrS copolymers possess an unanticipated additional gradient in stereosequence that parallels their comonomer gradient, that is, as the concentration of pBrs units decreases from one end of the copolymer chain to the other, so does the content of r diads. This conclusion could only be reached by comparison of observed and calculated Kerr effects, which access the global properties of macromolecules, and not NMR, which is only sensitive to local polymer structural environments, but not to their locations on the copolymer chains. Molar Kerr constants are characteristic of entire polymer chains and are highly sensitive to their constituent microstructures and their distribution along the chain. They may be used to both identify constituent microstructures and locate them along the polymer chain, thereby enabling, for the first time, characterization of their complete macrostructures. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013}, number={9}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Hardrict, S. N. and Gurarslan, R. and Galvin, C. J. and Gracz, H. and Roy, D. and Sumerlin, B. S. and Genzer, J. and Tonelli, A. E.}, year={2013}, month={May}, pages={735–741} }
 @article{kopyshev_galvin_genzer_lomadze_santer_2013, title={Opto-Mechanical Scission of Polymer Chains in Photosensitive Diblock-Copolymer Brushes}, volume={29}, ISSN={["0743-7463"]}, DOI={10.1021/la403241t}, abstractNote={In this paper we report on an opto-mechanical scission of polymer chains within photosensitive diblock-copolymer brushes grafted to flat solid substrates. We employ surface-initiated polymerization of methylmethacrylate (MMA) and t-butyl methacrylate (tBMA) to grow diblock-copolymer brushes of poly(methylmethacrylate-b-t-butyl methacrylate) following the atom transfer polymerization (ATRP) scheme. After the synthesis, deprotection of the PtBMA block yields poly(methacrylic acid) (PMAA). To render PMMA-b-PMAA copolymers photosensitive, cationic azobenzene containing surfactants are attached to the negatively charged outer PMAA block. During irradiation with an ultraviolet (UV) interference pattern, the extent of photoisomerization of the azobenzene groups varies spatially and results in a topography change of the brush, i.e., formation of surface relief gratings (SRG). The SRG formation is accompanied by local rupturing of the polymer chains in areas from which the polymer material recedes. This opto-mechanically induced scission of the polymer chains takes place at the interfaces of the two blocks and depends strongly on the UV irradiation intensity. Our results indicate that this process may be explained by employing classical continuum fracture mechanics, which might be important for tailoring the phenomenon for applying it to poststructuring of polymer brushes.}, number={45}, journal={LANGMUIR}, author={Kopyshev, Alexey and Galvin, Casey J. and Genzer, Jan and Lomadze, Nino and Santer, Svetlana}, year={2013}, month={Nov}, pages={13967–13974} }
 @misc{galvin_genzer_2012, title={Applications of surface-grafted macromolecules derived from post-polymerization modification reactions}, volume={37}, ISSN={["1873-1619"]}, DOI={10.1016/j.progpolymsci.2011.12.001}, abstractNote={The formation of functional polymers by implementing small-molecule organic chemistry reactions to homopolymers has attracted great attention lately due to an increasing number of novel potential applications. This post-polymerization modification (PPM) approach circumvents a number of problems associated with direct polymer synthesis and enables the creation of polymeric systems that are difficult or impossible to produce otherwise. This holds especially true in the field of polymer brushes where the tethering of the polymer chains to a surface complicates direct polymerization of bulky monomers. The advantages of PPM reactions do not stop with polymer synthesis. This review highlights a variety of innovations that stem directly from this approach. A selection of these applications includes modified barrier properties, catalysis, surface patterning, separations, and biologically active substrates.}, number={7}, journal={PROGRESS IN POLYMER SCIENCE}, author={Galvin, Casey J. and Genzer, Jan}, year={2012}, month={Jul}, pages={871–906} }