@article{kopyshev_kanevche_lomadze_pfitzner_loebner_patil_genzer_heberle_santer_2019, title={Light-Induced Structuring of Photosensitive Polymer Brushes}, volume={1}, ISSN={["2637-6105"]}, DOI={10.1021/acsapm.9b00705}, abstractNote={We investigate light-induced irreversible structuring of surface topographies in poly(3-sulfopropyl methacrylate/potassium salt) (PSPMK) brushes on flat solid substrates prepared by surface-initiated atom transfer radical polymerization. The brushes have been loaded with azobenzene-based surfactant comprised of positively charged headgroups and hydrophobic tail. The surfactant exhibits photoresponsive properties through photoisomerization from the trans to cis states leading to significant changes in physicochemical properties of grafted polymer chains. The azobenzene surfactant enables photoresponsive behavior without introducing irreversible changes to chemical composition of the parent polymer brush. Exposing these photosensitive brushes to irradiation with UV interference beams causes the polymer brush to form surface relief grating (SRG) patterns. The cationic surfactant penetrates only ∼25% of the upper portion of the PSPMK brush, resulting in the formation of two sections within the brush: a photor...}, number={11}, journal={ACS APPLIED POLYMER MATERIALS}, author={Kopyshev, Alexey and Kanevche, Katerina and Lomadze, Nino and Pfitzner, Emanuel and Loebner, Sarah and Patil, Rohan R. and Genzer, Jan and Heberle, Joachim and Santer, Svetlana}, year={2019}, month={Nov}, pages={301–3026} }
 @article{patil_miles_ko_datta_rao_kiserow_genzer_2018, title={Kinetic Study of Degrafting Poly(methyl methacrylate) Brushes from Flat Substrates by Tetrabutylammonium Fluoride}, volume={51}, ISSN={["1520-5835"]}, DOI={10.1021/acs.macromol.8b01832}, abstractNote={Polymer degrafting is a process in which surface-attached polymer brushes are removed from the substrate by breaking a chemical bond in proximity to the substrate. This paper provides insight into the kinetics of degrafting poly(methyl methacrylate) (PMMA) brushes using tetrabutylammonium fluoride (TBAF) and demonstrates how the process can be modeled using a series of degrafting reactions. The trichlorosilane-based polymerization initiator utilized here to synthesize PMMA grafts by surface-initiated atom transfer radical polymerization anchors to the silica substrate by up to three potential attachment points. During the degrafting sequence this anchoring reduces to two and one chemical bond and finally results in complete liberation of the PMMA macromolecule from the substrate. We investigate the effect of TBAF concentration, the initial grafting density of PMMA grafts on the substrate, and TBAF exposure time on degrafting of PMMA by monitoring the instantaneous areal grafting density of PMMA on the sub...}, number={24}, journal={MACROMOLECULES}, author={Patil, Rohan and Miles, Jason and Ko, Yeongun and Datta, Preeta and Rao, Balaji M. and Kiserow, Douglas and Genzer, Jan}, year={2018}, month={Dec}, pages={10237–10245} }
 @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{patil_kiserow_genzer_2015, title={Creating surface patterns of polymer brushes by degrafting via tetrabutyl ammonium fluoride}, volume={5}, ISSN={["2046-2069"]}, DOI={10.1039/c5ra17000a}, abstractNote={We demonstrate the use of tetrabutyl ammonium fluoride (TBAF) for creating spatial patterns of poly(methyl methacrylate) (PMMA) brushes on a flat silica support by degrafting PMMA grafted chains from selected regions on the substrate.}, number={105}, journal={RSC ADVANCES}, author={Patil, Rohan and Kiserow, Douglas and Genzer, Jan}, year={2015}, pages={86120–86125} }
 @article{patil_turgman-cohen_srogl_kiserow_genzer_2015, title={Direct Measurement of Molecular Weight and Grafting Density by Controlled and Quantitative Degrafting of Surface-Anchored Poly(methyl methacrylate)}, volume={4}, ISSN={["2161-1653"]}, DOI={10.1021/mz5007188}, abstractNote={We report on quantitative determination of the molecular weight distribution (MWD) and grafting density (σP) of polymer assemblies grown by controlled radical polymerization from flat substrates as a function of polymerization time and the ratio between the inhibitor and catalyst species. Specifically, we grow poly(methyl methacrylate) (PMMA) brushes on flat silica-based surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP), cleave the PMMA grafts quantitatively using tetrabutyl ammonium fluoride (TBAF), and analyze their MWD by size exclusion chromatography equipped with a high-sensitivity differential refractive index detector. The polymer growth and degrafting processes are followed by ellipsometry, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. The σP is independent of polymerization time and increases with increasing SI-ATRP inhibitor/catalyst ratio. Specifically, σP increases from 0.48 ± 0.06 to 0.58 ± 0.06 chains/nm2 as the inhibitor/catalyst molar ratio increases from 0 to 0.015, respectively, providing evidence that high inhibitor/catalyst ratio offers better control of the SI-ATRP reaction, by lowering number of terminations, and leading to denser PMMA brush assemblies.}, number={2}, journal={ACS MACRO LETTERS}, author={Patil, Rohan R. and Turgman-Cohen, Salomon and Srogl, Jiri and Kiserow, Douglas and Genzer, Jan}, year={2015}, month={Feb}, pages={251–254} }
 @article{patil_turgman-cohen_srogl_kiserow_genzer_2015, title={On-Demand Degrafting and the Study of Molecular Weight and Grafting Density of Poly(methyl methacrylate) Brushes on Flat Silica Substrates}, volume={31}, ISSN={["0743-7463"]}, DOI={10.1021/la5044766}, abstractNote={We report on degrafting of surface-anchored poly(methyl methacrylate) (PMMA) brushes from flat silica-based substrates using tetrabutylammonium fluoride (TBAF) and determining their molecular weight distribution (MWD) using size exclusion chromatography (SEC). The grafted PMMA layer was synthesized using surface-initiated atom transfer radical polymerization (SI-ATRP) of MMA for polymerization times ranging from 6 to 24 h. X-ray photoelectron spectroscopy, ellipsometry, and time-of-flight secondary ion mass spectrometry were employed in tandem to characterize the degrafting process. The SEC eluograms were fit to various polymer distributions, namely Zimm-Schulz, ATRP in continuous stirred tank reactor, Wesslau, Schulz-Flory, and Smith et al. The ATRP model gives the best fit to the experimental data. The dry PMMA brush thickness and the number-average molecular weight (obtained from the MWD) suggest that the grafting density of the PMMA grafts is independent of polymerization time, indicating well-controlled/living growth of MMA. The observed polydispersity index (PDI) was higher than that generally observed in bulk grown polymers under similar conditions, indicating an effect due to chain confinement and crowding. We detect small but noticeable dependence of the polymer brush grafting density on the inhibitor/catalyst ratio. Higher inhibitor/catalyst ratio offers better control with lower early terminations, which results in a small increase in the apparent grafting density of the chains.}, number={8}, journal={LANGMUIR}, author={Patil, Rohan R. and Turgman-Cohen, Salomon and Srogl, Jiri and Kiserow, Douglas and Genzer, Jan}, year={2015}, month={Mar}, pages={2372–2381} }