UVM Theses and Dissertations
Format:
Print
Author:
Murphy, Karen A.
Dept./Program:
Chemistry
Year:
2007
Degree:
MS
Abstract:
The adsorption of the synthesized PEO-PLA block copolymers micelles onto colloidal polystyrene (CPS) was determined using DLS. The adlayer thickness of the block copolymer layer on the surface was measured by subtraction of the colloidal radius from the combined adsorbed polymer and CPS radius. The mechanism for adsorption occurs in three main steps; (1) the adsorption of unimers onto the hydrophobic surface (2) surface rearrangement of the unimers and (3) adoption of the energetically favored conformation. In general, adlayer thickness behaves qualitatively as expected. The copolymers do not appear to adsorb onto the small colloid (R[subscript h] = 13.6 nm) instead it is believed to be encapsulated by the hydrophobic block.
This is reflected in an extremely elevated aggregate Rh. The intermediate colloid (R[subscript h] = 29.3 nm) appears to have been encapsulated at small weight fractions of PEO (20-40%) and appear to undergo adsorption at high weight fractions of PEO (40-80%). This change in adsorption properties may be due to a change in morphology. The block copolymers appear to adsorb to the surface of the large colloids (R[subscript h] = 39.6, 50.0, 134.5 nm) at any weight fraction of PEO. All of these results were confirmed by light scattering.
The experiments determining adlayer thickness were compared to the planar brush, star, discrete blob, and density distribution models. It was found that the star and model best described the some of the large colloids (R[subscript h] = 29.3, 39.6,50.0 nm). Finally, the alternative initiator iron (II) acetate was compared to the standard initiator, stannous octoate, to see if this greener initiator could be used instead. However, it was found that the catalyst did not convert monomer to polymer as efficiently as stannous octoate used originally.
This is reflected in an extremely elevated aggregate Rh. The intermediate colloid (R[subscript h] = 29.3 nm) appears to have been encapsulated at small weight fractions of PEO (20-40%) and appear to undergo adsorption at high weight fractions of PEO (40-80%). This change in adsorption properties may be due to a change in morphology. The block copolymers appear to adsorb to the surface of the large colloids (R[subscript h] = 39.6, 50.0, 134.5 nm) at any weight fraction of PEO. All of these results were confirmed by light scattering.
The experiments determining adlayer thickness were compared to the planar brush, star, discrete blob, and density distribution models. It was found that the star and model best described the some of the large colloids (R[subscript h] = 29.3, 39.6,50.0 nm). Finally, the alternative initiator iron (II) acetate was compared to the standard initiator, stannous octoate, to see if this greener initiator could be used instead. However, it was found that the catalyst did not convert monomer to polymer as efficiently as stannous octoate used originally.