Buckling into single-handed chiral structures from pH-sensitive hydrogel membranes. (June 2016)

• Record Type: Journal Article
• Authors: Cao, Bo; Wu, Gaoxiang; Xia, Yu; Yang, Shu
• Is Part Of: Extreme mechanics letters. Volume 7(2016)
• Page Start: 49
• Page End: 54
• Publication Date: 2016-06
• Subjects: Swelling induced pattern transformation -- Pre-stretching -- Single-handed chirality; Mechanics -- Periodicals; Mechanics, Applied -- Periodicals; Mechanics; Electronic journals; Periodicals; 531.05
• DOI: 10.1016/j.eml.2015.12.011
• Languages: English
• ISSNs: 2352-4316

Abstract

Abstract: We investigate swelling induced pattern transformation of pH-sensitive hydrogel membranes made of poly(2-hydroxyethyl methacrylate)- co -poly(acrylic acid) (PHEMA- co -PAA) with periodic pores in both square and oblique arrays. The hydrogel membranes are fabricated by replica molding from a poly(dimethylsiloxane) (PDMS) mold with square arrayed pillars, or from the same mold that is mechanically pre-stretched at a very small strain (5%) at different angles (15 °, 30 °, 45 °, 60 °, and 75 ° ) relative to the lattice axis. When swollen in different pH buffer solutions, the membrane undergoes buckling of pores to slits at pH 3 (achiral, swelling ratio ∼2.0) to onset of symmetry breaking of slits at pH 4.7 (swelling ratio ∼2.3), to the formation of twisted, "S" shaped slits at pH 6.4 (chiral, swelling ratio ∼5.8). While swelling of the square array hydrogel membranes leads to ∼50/50 mixture of right- and left-handed chiral structures, predominant single handedness with enantiomeric excess fraction >95% (i.e. the absolute difference between the mole fraction of each enantiomer) is obtained from the oblique array of porous membranes. Single left-handedness is obtained from the ones with low pre-stretching angles (15 ° and 30 ° ), while nearly exclusive right-handedness is obtained from the ones with larger pre-stretching angles (60 ° and 75 ° ).