Force Interactions of Nonagglomerating Polylactide
Particles Obtained through Covalent Surface Grafting with Hydrophilic
Polymers
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Abstract
Nonagglomerating polylactide (PLA)
particles with various interaction
forces were designed by covalent photografting. PLA particles were
surface grafted with hydrophilic poly(acrylic acid) (PAA) or poly(acrylamide)
(PAAm), and force interactions were determined using colloidal probe
atomic force microscopy. Long-range repulsive interactions were detected
in the hydrophilic/hydrophilic systems and in the hydrophobic/hydrophilic
PLA/PLA-<i>g</i>-PAAm system. In contrast, attractive interactions
were observed in the hydrophobic PLA/PLA and in the hydrophobic/hydrophilic
PLA/PLA-<i>g</i>-PAA systems. AFM was also used in the tapping
mode to determine the surface roughness of both neat and surface-grafted
PLA film substrates. The imaging was performed in the dry state as
well as in salt solutions of different concentrations. Differences
in surface roughness were identified as conformational changes induced
by the altered Debye screening length. To understand the origin of
the repulsive force, the AFM force profiles were compared to the Derjaguin,
Landau, Verwey, and Overbeek (DLVO) theory and the Alexander de Gennes
(AdG) model. The steric repulsion provided by the different grafted
hydrophilic polymers is a useful tool to inhibit agglomeration of
polymeric particles. This is a key aspect in many applications of
polymer particles, for example in drug delivery