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Buckling into single-handed chiral structures from pH-sensitive hydrogel membranes

Extreme Mechanics Letters, ISSN: 2352-4316, Vol: 7, Page: 49-54
2016
  • 11
    Citations
  • 0
    Usage
  • 30
    Captures
  • 0
    Mentions
  • 0
    Social Media
Metric Options:   Counts1 Year3 Year

Metrics Details

  • Citations
    11
    • Citation Indexes
      11
  • Captures
    30

Article Description

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 ° ).

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