Using Liquid Crystals to Probe the Organization of Helical Polypeptide Brushes Induced by Solvent Pretreatment

Abstract

Grafted polymer brushes form the basis of a versatile class of surfaces with properties that can be tailored via choice of the chemical functional groups or architecture of the grafted polymers. Here, we explore how treatment by solvents can program the organization of homopolymer brushes comprising helical poly(γ-benzyl-Lglutamate) (PBLG) and how the orientational behavior of liquid crystals (LCs) contacted with the brushes can provide fresh insights into brush organization. We treated PBLG brushes with either good (chloroform) or poor (acetone) solvents to form collapsed or teepee-like grafted polymer organizations, respectively. When supported on PBLG brushes with thicknesses [determined by atomic force microscopy (AFM)] of 50 nm, we found that collapsed and teepee-like brushes induced planar (parallel to surface) and homeotropic (perpendicular to surface) orientations of nematic LCs, respectively. By preparing solvent-pretreated brushes with a range of thicknesses (12−140 nm), and by combining insights based on AFM, Fourier-transform infrared spectroscopy and LCs, we found that a continuous change in tilt of the LC is accompanied by a continuous change in tilt of the PBLG chains, as influenced by the teepee-like organization. The role of PBLG chain orientation in dictating the LC orientation was confirmed by additional experiments in which PBLG brushes were thermally denatured. Finally, when using mixed solvents (mixtures of chloroform and acetone) to manipulate the PBLG brush organization, we observed LCs to exhibit patterned orientations on the micrometer scale, consistent with patterned orientations of the PBLG chains imprinted by droplets formed during the mixed solvent drying process. Overall, these results expand our understanding of the range of PBLG brush organizations that can be induced by solvent pretreatment and demonstrate the utility of LCs for imaging PBLG chain orientation within brushes.

Adaptive 2D and Pseudo-2D Systems: Molecular, Polymeric, and Colloidal Building Blocks for Tailored Complexity

“…Polymeric systems (either nano-or sub-micron) have been investigated regarding their dynamic self-assembly and adaptiveness to environmental changes [69,76,[92][93][94]. The adaptability comes from a variety of triggers, ranging from light excitation and field gradient (temperature, magnetic, electric potential) to chemical methods (presence or lack of specific compounds or a gradient of concentration) [95][96][97].…”

Self-assembly of rod–coil–rod block copolymers in a coil-selective solvent: coarse-grained simulation results

“…[1][2][3][4] These polymer materials have found applications in several fields including organic electronics, 5-7 optoelectronics [8][9][10] and biomedical sciences. 11 Rigid chain conformations originate from a reduced chain flexibility that can arise by several factors, for example by p-conjugation along the polymer backbone 4 or helical secondary structures in the case of biomacromolecules; 12 aromatic groups can also lead to rigid, extended conformations. 1 The self-assembly of block copolymers that include rod-like blocks is fundamentally different from that of all-coil block copolymers because of the effect of chain rigidity on conformational entropy and molecular packing.…”