Abstract:

Triblock copolymer, poly(D-lactide)-b-polydimethylsiloxane-b-poly(D-lactide)(PDLA-b-PDMS-b-PDLA), was synthesized by ring-opening polymerization of D-lactide, and then its solution was coated onto the surface of poly(L-lactide)(PLLA) in a vail filled with non-solvent vapor. During the slow deposition process, PDMS with low surface energy was introduced to the PLLA surface. Meanwhile, PDLA segments stereocomplexed with the PLLA segments on the surface. A hydrophobic layer composed of stereocomposite submicron particles was formed on the surface of PLLA through the stereocomplexation between PLLA and PDLA-b-PDMS-b-PDLA and the self-assembly of PDLA-b-PDMS-b-PDLA. The influences of polymer solution concentration, assembly temperature and solvent on the surface morphology and the hydrophobicity of PLLA surface were further studied. With the increase of the concentration of PDLA-b-PDMS-b-PDLA, the hydrophobic behavior of the surface showed a transformation from Wenzel to Cassie status, and then returned to Wenzel status. When the assembly temperature was 0 ℃ and a 2 g/L PDLA-b-PDMS-b-PDLA/CH₂Cl₂ solution was deposited on the PLLA surface, the contact angle was 151°. When the assembly temperature raised to 30 ℃, the surface contact angle was 144° and the rolling angle was 5°. The obtained surface morphology and hydrophobicity were also varied with solvents with different solubility and volatilization rate. In addition, the hydrophobic surface of PLLA products can be achieved by means of stereocomplexation and self-assembly. By varying the concentration of PDLA-b-PDMS-b-PDLA solutions, the surface of PLLA products would eventually assembles into a “pearl necklace” shaped bicontinuous network structure. Because the surface of PLLA and the submicron particles were all connected with stereocomplexed PLLA/PDLA chains, the hydrophobic layer exhibited good durability against knife-scratch, tape-peel and finger-wipe tests. After the knife-scratch test and the tape peel test, the contact angle of the surface of the PLLA products was only slightly reduced, and the micro-spherical appearance of the PLLA surface existed after test.

Key words: poly(L-lactide), stereocomplex, self-assembly, hydrophobic surface