@article{genzer_arifuzzaman_bhat_efimenko_ren_szleifer_2012, title={Time Dependence of Lysozyme Adsorption on End-Grafted Polymer Layers of Variable Grafting Density and Length}, volume={28}, ISSN={["0743-7463"]}, DOI={10.1021/la2038747}, abstractNote={A combined experimental and theoretical approach establishes the long-lived nature of protein adsorption on surfaces coated with chemically grafted macromolecules. Specifically, we monitor the time dependence of adsorption of lysozyme on surfaces comprising polymer assemblies made of poly(2-hydroxyethyl methacrylate) brushes grafted onto flat silica surfaces such that they produce patterns featuring orthogonal and gradual variation of the chain length (N) and grafting density (σ). We show that in the kinetically controlled regime, the amount of adsorbed protein scales universally with the product σN, while at equilibrium the amount of adsorbed protein is governed solely by σ. Surprisingly, for moderate concentrations of protein in solution, adsorption takes more than 72 h to reach an equilibrium, or steady state. Our experimental findings are corroborated with predictions using molecular theory that provides further insight into the protein adsorption phenomenon. The theory predicts that the universal behavior observed experimentally should be applicable to polymers in poor and theta solvents and to a limited extent also to good solvent conditions. Our combined experimental and theoretical findings reveal that protein adsorption is a long-lived phenomenon, much longer than generally assumed. Our studies confirm the previously predicted important differences in behavior for the kinetic versus thermodynamic control of protein adsorption.}, number={4}, journal={LANGMUIR}, author={Genzer, Jan and Arifuzzaman, Shafi and Bhat, Rajendra R. and Efimenko, Kirill and Ren, Chun-lai and Szleifer, Igal}, year={2012}, month={Jan}, pages={2122–2130} }
 @misc{genzer_bhat_2008, title={Surface-bound soft matter gradients}, volume={24}, ISSN={["0743-7463"]}, DOI={10.1021/la7033164}, abstractNote={This feature article describes the progress realized over the past half century in the field of surface-bound gradient structures created on or from soft materials (oligomers and/or polymers), or those enabling the study of the behavior of soft materials. By highlighting our work in the field and accounting for the contribution of other groups, we emphasize the exceptional versatility of gradient assemblies in facilitating fast screening of physicochemical phenomena, acting as "recording media" for monitoring a process, and playing a key role in the design and fabrication of surface-bound molecular and macromolecular motors capable of directing a transport phenomenon.}, number={6}, journal={LANGMUIR}, author={Genzer, Jan and Bhat, Rajendra R.}, year={2008}, month={Mar}, pages={2294–2317} }
 @article{jhon_bhat_jeong_rojas_szleifer_genzer_2006, title={Salt-induced depression of lower critical solution temperature in a surface-grafted neutral thermoresponsive polymer}, volume={27}, ISSN={["1521-3927"]}, DOI={10.1002/marc.200600031}, abstractNote={AbstractSummary: Quartz crystal microbalance with dissipation monitoring (QCM‐D) is employed to determine the effect of salt on the volume phase transition of thermoresponsive polymer brushes. Changes in mass and viscoelasticity of poly(N‐isopropylacrylamide) (PNIPAM) layers grafted from a QCM‐D crystal are measured as a function of temperature, upon contact with aqueous solutions of varying salt concentrations. The phase‐transition temperature of PNIPAM brushes, TC,graft, quantified from the QCM‐D measurements is found to decrease as the concentration of salt is increased. This phenomenon is explained by the tendency of salt ions to affect the structure of water molecules (Hofmeister effect). However, in contrast to the linear decrease in phase‐transition temperature upon increasing salt concentration observed for free PNIPAM, the trend in TC,graft for PNIPAM brushes is distinctively non‐linear.Schematic representation of the effect of salt concentration on the phase transition behavior of thermoresponsive polymer brushes.magnified imageSchematic representation of the effect of salt concentration on the phase transition behavior of thermoresponsive polymer brushes.
}, number={9}, journal={MACROMOLECULAR RAPID COMMUNICATIONS}, author={Jhon, Young K. and Bhat, Rajendra R. and Jeong, Changwoo and Rojas, Orlando J. and Szleifer, Igal and Genzer, Jan}, year={2006}, month={May}, pages={697–701} }
 @article{bhat_tomlinson_wu_genzer_2006, title={Surface-grafted polymer gradients: Formation, characterization, and applications}, volume={198}, ISBN={["3-540-30251-4"]}, ISSN={["1436-5030"]}, DOI={10.1007/12_060}, journal={SURFACE- INITIATED POLYMERIZATION II}, publisher={Berlin; New York: Springer}, author={Bhat, Rajendra R. and Tomlinson, Michael R. and Wu, Tao and Genzer, Jan}, year={2006}, pages={51–124} }
 @article{bhat_genzer_2007, title={Tuning the number density of nanoparticles by multivariant tailoring of attachment points on flat substrates}, volume={18}, ISSN={["0957-4484"]}, DOI={10.1088/0957-4484/18/2/025301}, abstractNote={We report on the organization of nanoparticles on a flat surface when there is strong yet tunable interaction between the particles and the surface. Specifically, we tailor the number density of citrate-stabilized gold nanoparticles on flat substrates by varying the concentration of the grafted amino groups on the surfaces and their degree of ionization. While the former effect is accomplished by decorating silica-based substrates with a molecular gradient of (3-aminopropyl)triethoxysilane (APTES), the latter effect is achieved by varying the degree of ionization of the −NH2 groups in APTES by varying the pH of the gold sol. We show that the measurement of particle number density on an APTES concentration gradient substrate at different pH values provides a simple, non-spectroscopic means to deduce the relative molecular concentration profile of APTES on the substrate.}, number={2}, journal={NANOTECHNOLOGY}, author={Bhat, Rajendra R. and Genzer, Jan}, year={2007}, month={Jan} }
 @article{bhat_genzer_2006, title={Combinatorial study of nanoparticle dispersion in surface-grafted macromolecular gradients}, volume={252}, ISSN={["0169-4332"]}, DOI={10.1016/j.apsusc.2005.03.237}, abstractNote={Surface-tethered assemblies of polymers with gradually varying molecular weight (MW) and/or grafting density are utilized to control the dispersion of nanosized particles. Using several case studies we show that these gradient polymer specimens represent ideal systems for combinatorial exploration of the parameters that control the distribution of the particles in surface-grafted layers. We demonstrate that the particle distribution is governed by the interplay between the particle size and the grafting density and molecular weight of the polymer brush.}, number={7}, journal={APPLIED SURFACE SCIENCE}, author={Bhat, RR and Genzer, J}, year={2006}, month={Jan}, pages={2549–2554} }
 @article{bhat_tomlinson_genzer_2005, title={Orthogonal surface-grafted polymer gradients: A versatile combinatorial platform}, volume={43}, ISSN={["1099-0488"]}, DOI={10.1002/polb.20640}, abstractNote={AbstractOrthogonal polymer brush gradients are assemblies of surface‐anchored macromolecules, in which two material properties of the grafted chains (e.g., grafting density, molecular weight) vary independently in orthogonal directions. Here, we describe the formation and applications of two such orthogonal assemblies, involving: (1) molecular weight and grafting density (MW/σ) gradients of a given polymer and (2) molecular weight gradients (MW1/MW2), of two different polymers. Each point on orthogonal gradient substrate represents a unique combination of the two surface properties being varied, thus facilitating systematic investigation of a phenomenon that depends on the two said properties. We illustrate this point by employing orthogonal structures to study systematically: (1) formation of polymer brush‐nanoparticle composite assemblies, (2) protein adsorption and cell adhesion, and (3) chain conformations in tethered diblock copolymers exposed to selective solvents. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3384–3394, 2005}, number={23}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Bhat, RR and Tomlinson, MR and Genzer, J}, year={2005}, month={Dec}, pages={3384–3394} }
 @article{bhat_chaney_rowley_liebmann-vinson_genzer_2005, title={Tailoring cell adhesion using surface-grafted polymer gradient assemblies}, volume={17}, ISSN={["1521-4095"]}, DOI={10.1002/adma.200500858}, abstractNote={higher-energy emissions due to impurity phases. In conclusion, well-defined [ZnSe](DETA)0.5 nanobelts have been synthesized successfully by tuning the composition of a ternary solution made of DETA, hydrazine hydrate, and deionized water. We find that an appropriate amount of hydrazine hydrate is essential for the formation of elegant [ZnSe](DETA)0.5 nanobelts. While the optical properties of the nanobelts are not changed significantly, the ability to make these II–VI-based hybrid semiconductor nanostructure microparticles into nanocrystals with uniform shape and size is one step further towards the miniaturization of devices. In addition, surface modification or combination with other materials may introduce new phenomena and properties into this system with remarkable quantum size effects and expand their potential for applications in advanced semiconductor devices.}, number={23}, journal={ADVANCED MATERIALS}, author={Bhat, RR and Chaney, BN and Rowley, J and Liebmann-Vinson, A and Genzer, J}, year={2005}, month={Dec}, pages={2802-+} }
 @article{bhat_genzer_2005, title={Using spectroscopic ellipsometry for quick prediction of number density of nanoparticles bound to non-transparent solid surfaces}, volume={596}, ISSN={["1879-2758"]}, DOI={10.1016/j.susc.2005.09.014}, abstractNote={We report on the use of spectroscopic ellipsometry (SE) in predicting number density of nanoparticles bound to the surfaces decorated with either organic monolayers or surface-grafted polymers. Two systems are considered that comprise citrate-stabilized gold nanoparticles adsorbed on: (1) 3-aminopropyltriethoxysilane (APTES) self-assembled monolayer (SAM), and (2) surface-tethered polyacrylamide (PAAm). Number density of gold nanoparticles on the surface is varied systematically by gradually increasing either the concentration of APTES molecules in the SAM or molecular weight of grafted PAAm. The adsorption of gold nanoparticles on APTES gradient surfaces is monitored via atomic force microscopy (AFM), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and SE. The partition of gold nanoparticles on PAAm gradient assemblies is characterized by AFM, ultraviolet–visible (UV–vis) spectroscopy, and SE. By correlating the results obtained from the various techniques on nanoparticle coatings, we derive an empirical linear relationship between the number density of nanoparticles on surfaces and cos (Δ) parameter measured in SE. Excellent agreement between nanoparticle number density determined experimentally from AFM scans and that predicted by SE proves the potential of SE as a quick, predictive technique to estimate number density of nanoparticles bound to solid, non-transparent substrates.}, number={1-3}, journal={SURFACE SCIENCE}, author={Bhat, RR and Genzer, J}, year={2005}, month={Dec}, pages={187–196} }
 @article{bhat_tomlinson_genzer_2004, title={Assembly of nanoparticles using surface-grafted orthogonal polymer gradients}, volume={25}, ISSN={["1521-3927"]}, DOI={10.1002/marc.200300163}, abstractNote={AbstractSummary: We report on preparing poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) gradient substrate, wherein molecular weight (MW) and grafting density (σ) of the surface‐anchored PDMAEMA chains vary continuously in two orthogonal directions. Such a specimen is used to control the assembly of charged gold nanoparticles. Increasing MW and σ of the grafted PDMAEMA cause an enhanced binding of the nanoparticles to PDMAEMA, thus leading to an orthogonal number density gradient of surface‐bound gold nanoparticles.magnified image}, number={1}, journal={MACROMOLECULAR RAPID COMMUNICATIONS}, author={Bhat, RR and Tomlinson, MR and Genzer, J}, year={2004}, month={Jan}, pages={270–274} }
 @article{bhat_genzer_chaney_sugg_liebmann-vinson_2003, title={Controlling the assembly of nanoparticles using surface grafted molecular and macromolecular gradients}, volume={14}, ISSN={["1361-6528"]}, DOI={10.1088/0957-4484/14/10/313}, abstractNote={We report on the generation of assemblies comprising number density gradients of nanoparticles in two (2D) and three (3D) dimensions. These structures are fabricated by creating a surface-bound organic template which directs the spatial arrangement of gold nanoparticles. The 2D template is made of amine-terminated organosilane with a concentration gradient along the solid substrate. The 3D matrix comprises surface-anchored poly(acryl amide), whose molecular weight changes gradually on the specimen. In both cases, the composite is assembled at low pH, where the positively charged –NH3+ groups within the organic scaffold attract negatively charged gold nanoparticles. We use a battery of experimental tools to determine the number density of particles along the gradient substrate and in the case of 3D structures also their spatial distribution. For 2D gradient assemblies, we show that gold nanoparticle coverage on the surface decreases gradually as the concentration of substrate-bound aminosilane decreases. The number of particles in the polymer brush/particle hybrid is found to increase with increasing polymer molecular weight. We show that for a given grafting density of polymer brush, larger particles predominantly stay near the brush–air interface. In contrast, smaller nanoparticles penetrate deeper into the polymer brush, thus forming a 3D structure. Finally, we discuss possible applications of these nanoparticle gradient assemblies.}, number={10}, journal={NANOTECHNOLOGY}, author={Bhat, RR and Genzer, J and Chaney, BN and Sugg, HW and Liebmann-Vinson, A}, year={2003}, month={Oct}, pages={1145–1152} }
 @article{fischer_efimenko_bhat_sambasivan_genzer_2004, title={Mapping surface chemistry and molecular orientation with combinatorial near-edge X-ray absorption fine structure spectroscopy}, volume={25}, ISSN={["1521-3927"]}, DOI={10.1002/marc.200300178}, abstractNote={AbstractSummary: Mapping the bond chemistry and molecular orientation of self‐assembled monolayer gradients on flat surfaces and reaction intermediates in catalyst arrays is made possible using combinatorial near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy. These spatially resolved NEXAFS maps have been made by utilizing synchrotron‐based NEXAFS spectroscopy in conjunction with a computer controlled precision sample manipulator. The NEXAFS maps reveal bond concentration, rehybridization, and orientation of the surface‐bound molecules with sub‐millimeter planar spatial resolution and sub‐monolayer molecular sensitivity. The wide applicability of the combinatorial NEXAFS method is illustrated by mapping: (1) the concentration and molecular orientation of semifluorinated molecules in molecular gradients; (2) the concentration of amino groups in molecular gradients used for nanoparticle templating, and (3) the rehybridization of propylene intermediates on zeolite catalyst arrays used for measuring solid‐state acidity and catalyst activity.The principle of “combinatorial” NEXAFS. The molecular gradient is indicated pictorially by the shading on the specimen.magnified imageThe principle of “combinatorial” NEXAFS. The molecular gradient is indicated pictorially by the shading on the specimen.
}, number={1}, journal={MACROMOLECULAR RAPID COMMUNICATIONS}, author={Fischer, DA and Efimenko, K and Bhat, RR and Sambasivan, S and Genzer, J}, year={2004}, month={Jan}, pages={141–149} }
 @misc{bhat_fischer_genzer_2002, title={Fabricating planar nanoparticle assemblies with number density gradients}, volume={18}, ISSN={["0743-7463"]}, DOI={10.1021/la025524m}, abstractNote={We report on preparing assemblies of gold nanoparticles with continuous gradients in number density on flat silica-covered substrates. The methodology consists of (i) first forming a one-dimensional molecular gradient of amino groups (−NH2) on the substrate by vapor deposition of amine-terminated silane molecules, followed by (ii) attachment of gold nanoparticles to −NH2 functional groups by immersing the substrate in a colloidal gold solution. Experiments using atomic force microscopy reveal that the number density of nanoparticles on the substrate varies continuously as a function of the position on the substrate. Near-edge X-ray absorption fine structure studies confirm that the nanoparticle number density gradient is closely correlated with the concentration gradient of −NH2 groups anchored to the substrate. We demonstrate that the number density of nanoparticles within the gradient and the length of the gradient can be tuned by controlling the vapor diffusion of silane molecules. In addition we show ...}, number={15}, journal={LANGMUIR}, author={Bhat, RR and Fischer, DA and Genzer, J}, year={2002}, month={Jul}, pages={5640–5643} }