Nanopatterning in Langmuir-Blodgett monolayers of a thermoresponsive double hydrophilic block copolymer studied by atomic force microscopy.
The microphase-separation of Langmuir-Blodgett (LB) monolayers of a rhodamine B (RhB) end-labeled double hydrophilic block copolymer (DHBC), RhB-Poly(N,N-dimethylacrylamide)-b-poly(N,N-diethylacryl-amide) (RhB-PDMA(207)b-PDEA177) and the 1:1 segmental mixture of PDEA and RhB-PDMA homopolymers was followed by AFM. The DHBC LB films revealed a loose distribution of nano-aggregates with variable geometries below the lower critical solution temperature (LCST) of PDEA (32 degrees C) and low surface pressure (3 mN m(-1)). By increasing either the temperature above the LCST of PDEA or the surface pressure beyond the immersion regime of PDMA in the subphase (7 mN m(-1)) a dense nanopatterning was obtained. The absence of a corresponding regular nanopatterning in LB films of mixed homopolymers with the same composition highlights the role of the covalent bonding between PDEA and PDMA on the self-segregation of the two blocks at the air-water interface.
Surface Micelle Structures and Monolayer Compression Moduli of Double Hydrophilic Block Copolymer
At the air/water interface, amphiphilic block copolymers are well-known to form typical surface micelles composed of hydrophobic block cores and hydrophilic block coronas. However, the micelle/aggr...
Achievements and contradictions of the Peruvian agrarian reform
Different paths of transition to capitalist agriculture, as well as different types of agrarian reform, can be distinguished. The Peruvian agrarian reform is analysed within this context and evaluated in terms of its contribution to rural development. The Peruvian case underlines the importance of understanding the rationality of the pre‐existent agrarian system for a successful restructuring of the agrarian economy and society. The contradictions which arose between the State's model and the peasants’ model of agrarian reform, as well as those between different types of peasants, are discussed. Peru's experience is also a reminder that a land reform is not a sufficient condition for rural development unless accompanied by proper price, marketing, credit and investment policies.