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pH-Responsive Polymer Nanoparticles Containing Pendant Carboxy and Sulfonate Groups
Sari Usuda1, Rintaro Takahashi2, Thi Ngan Vu1
1Department of Applied Chemistry, Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2201, Japan.
Langmuir : the ACS Journal of Surfaces and Colloids
|March 20, 2026
Summary
pH-responsive nanoparticles (P(AaHn/AMPS)NPs) were developed for controlled release applications. These nanoparticles exhibit significant swelling and size changes in response to pH variations, enabling efficient encapsulation and release of hydrophobic molecules.
Area of Science:
- Materials Science
- Polymer Chemistry
- Nanotechnology
Background:
- Development of pH-responsive materials is crucial for controlled drug delivery and sensing.
- Existing nanoparticles often lack stability across a broad pH range or exhibit slow response times.
- Need for adaptable nanocarriers capable of encapsulating and releasing hydrophobic molecules based on environmental pH.
Purpose of the Study:
- To synthesize and characterize novel pH-responsive nanoparticles (P(AaHn/AMPS)NPs) using 6-acrylamidohexanoic acid (AaH) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).
- To investigate the pH-dependent swelling, particle size changes, and guest molecule release capabilities of these nanoparticles.
- To evaluate the colloidal stability and response kinetics of the synthesized nanoparticles.
Main Methods:
- Soap-free emulsion polymerization was employed to synthesize P(AaHn/AMPS)NPs with varying AaH content (n = 89, 79, 59 mol %).
- Dynamic light scattering (DLS) and zeta potential measurements were used to analyze particle size and surface charge.
- Continuous-flow mixing method was utilized to determine the pH-response kinetics.
Main Results:
- P(AaHn/AMPS)NPs demonstrated improved colloidal stability across a wide pH range due to the incorporation of AMPS.
- At pH ≤ 6.4, nanoparticles decreased in size, enabling encapsulation of hydrophobic molecules like N-phenyl-1-naphthylamine.
- At pH > 6.4, nanoparticles swelled significantly (e.g., P(AaH89/AMPS)NPs showed a 137-fold volume increase), releasing encapsulated molecules. Response times were rapid, between 1.16-2.37 s, with faster acidification than basification.
Conclusions:
- The synthesized P(AaHn/AMPS)NPs are effective pH-responsive nanocarriers with tunable swelling and release properties.
- Higher AaH content correlates with greater changes in swelling and zeta potential, offering control over nanoparticle behavior.
- These nanoparticles show promise for applications requiring rapid and precise pH-triggered release of hydrophobic substances.
