Multiresponsive Clay-Containing Layer-by-Layer Films

We report on polymer/clay layer-by-layer films responsive to multiple stimuli. Temperature- and salt-responsive films were constructed using assembly of poly(N-isopropylacrylamide) (PNIPAM) and montmorillonite clay nanosheets. An additional pH response was achieved by depositing and cross-linking hy...

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Bibliographic Details
Published in:ACS nano 2011-11, Vol.5 (11), p.8790-8799
Main Authors: Zhuk, Aliaksandr, Mirza, Robert, Sukhishvili, Svetlana
Format: Article
Language:English
Subjects:
Acrylic Resins - chemistry
Aluminum Silicates - chemistry
Clay (material)
Collapse
Crosslinking
Dextrans
Hydrogen-Ion Concentration
Inclusions
Molecular Weight
Multilayers
Nanostructure
Nanotechnology - methods
Permeability
Salts - chemistry
Temperature
Water - chemistry
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Summary:We report on polymer/clay layer-by-layer films responsive to multiple stimuli. Temperature- and salt-responsive films were constructed using assembly of poly(N-isopropylacrylamide) (PNIPAM) and montmorillonite clay nanosheets. An additional pH response was achieved by depositing and cross-linking hybrid, dual-network PNIPAM/clay/PNIPAM/poly(methacrylic acid) (PMAA) multilayers. Both types of films remained stable in a wide pH range and were highly swollen. For example, PNIPAM/clay films swelled up to ∼14.5 times their dry film thickness in low-salt solutions at 25 °C, as shown by laser scanning confocal microscopy. At temperatures higher than PNIPAM’s lower critical solution temperature (LCST) of 32 °C, or in 0.3 M Na2SO4 solutions at room temperature, both PNIPAM/clay and PNIPAM/clay/PNIPAM/PMAA films reversibly deswelled as a result of collapse of PNIPAM chains. Films of both types showed a decrease in permeability to fluorescein-tagged dextrans of various molecular weights. Importantly, film permeability to dextrans was decreased at temperatures above PNIPAM’s LCST, and the effect could be reversed by lowering the temperature. Inclusion of PMAA within multilayers provided an additional pH response to film swelling and permeability. Hybrid PNIPAM/clay/PNIPAM/PMAA films showed drastic deswelling at low pH values due to the onset of hydrogen bonding between PNIPAM and PMAA, and the diffusion of 70 kDa dextran through multilayers at acidic pH was completely blocked. These multiresponse features of clay-containing films make them promising candidates for applications in sensing, actuation, and controlled delivery.
ISSN:1936-0851
1936-086X
DOI:10.1021/nn202812a