Probing soft polymeric coatings of a capillary by atomic force microscopy

Area of Science:

• Surface science
• Analytical chemistry
• Polymer science

Background:

• Capillary coating with soft polymers like polyacrylamides aims to reduce electroosmotic flow (EOF).
• EOF is problematic for separating macromolecules in capillary electrophoresis.
• Surface coverage quality is influenced by temperature and pH.

Purpose of the Study:

• To investigate the efficiency of polyacrylamide coating on silica capillary surfaces.
• To determine the impact of temperature and pH on coating effectiveness and EOF reduction.

Main Methods:

• Atomic Force Microscopy (AFM) was used to analyze capillary surface coverage.
• Direct measurement of electroosmotic flow (EOF) in coated and uncoated capillaries under an electric field.

Main Results:

• Higher temperatures (above 50°C) lead to incomplete polymer binding and exposed silica patches.
• High pH (10-11) during polymerization causes hydrolysis, hindering efficient coating.
• Low temperatures (10°C) and buffered pH 7 ensure thorough coating and near-elimination of EOF.
• Coated capillaries showed residual EOF values of 10⁻⁷ cm² V⁻¹ s⁻¹, compared to 10⁻⁴ cm² V⁻¹ s⁻¹ for uncoated ones.

Conclusions:

• Optimizing temperature and pH is critical for effective polyacrylamide coating of silica capillaries.
• Low-temperature (10°C) and neutral pH (7) polymerization conditions yield superior surface coverage.
• Efficient capillary coating significantly minimizes EOF, enhancing macromolecule separation quality.