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To tailor the nanomorphology in polymer/fullerene blends, we study the effect of electrostatic field (E-field) on the solidification of poly(3-hexylthiophene-2, 5-diyl) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) bulk heterojunction (BHJ). In addition to control; wet P3HT:PC60BM thin films were exposed to E-field of Van de Graaff (VDG) generator at three different directionshorizontal (H), tilted (T), and vertical (V)relative to the plane of the substrate. Surface and bulk characterizations of the field-treated BHJs affirmed that fullerene molecules can easily penetrate the spaghetti-like P3HT and move up and down following the E-field. Using E-field treatment, we achieved favorable morphologies with efficient charge separation, transport, and collection. We improve; (1) the hole mobility values up to 19.4 × 10–4± 1.6 × 10–4cm2V–1s–1and (2) the power conversion efficiency (PCE) of conventional and inverted OPVs up to 2.58 ± 0.02% and 4.1 ± 0.40%, respectively. This E-field approach can serve as a new morphology-tuning technique, which is generally applicable to other polymer–fullerene systems.

Ceramide-1-phosphate, the phosphorylated form of ceramide, gained attention recently due to its diverse intracellular roles, in particular in inflammation mediated by cPLA2α. However, surprisingly little is known about the physical chemical properties of this lipid and its potential impact on physiological function. For example, the presence of Ca2+is indispensable for the interaction of Cer-1-P with the C2 domain of cPLA2α. We report on the structure and morphology of Cer-1-P in monomolecular layers at the air/water solution interface in the absence and presence of Ca2+using diverse biophysical techniques, including synchrotron x-ray reflectivity and grazing angle diffraction, to gain insight into the role and function of Cer-1-P in biomembranes. We show that relatively small changes in pH and the presence of monovalent cations dramatically affect the behavior of Cer-1-P. On pure water Cer-1-P forms a solid monolayer despite the negative charge of the phosphomonoester headgroup. In contrast, pH 7.2 buffer yields a considerably less solid-like monolayer, indicating that charge-charge repulsion becomes important at higher pH. Calcium was found to bind strongly to the headgroup of Cer-1-P even in the presence of a 100-fold larger Na+concentration. Analysis of the x-ray reflectivity data allowed us to estimate how much Ca2+is bound to the headgroup, ∼0.5 Ca2+and ∼1.0 Ca2+ions per Cer-1-P molecule for the water and buffer subphase respectively. These results can be qualitatively understood based on the molecular structure of Cer-1-P and the electrostatic/hydrogen-bond interactions of its phosphomonoester headgroup. Biological implications of our results are also discussed.

Monomolecular films of valine gramicidin A (VGA) were investigated in situ at the air-water interface by x-ray reflectivity and x-ray grazing incidence diffraction as well as polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). These techniques were combined to obtain information on the secondary structure and the orientation of VGA and to characterize the shoulder observed in its π-Aisotherm. The thickness of the film was obtained by x-ray reflectivity, and the secondary structure of VGA was monitored using the frequency position of the amide I band. The PM-IRRAS spectra were compared with the simulated ones to identify the conformation adopted by VGA in monolayer. At large molecular area, VGA shows a disordered secondary structure, whereas at smaller molecular areas, VGA adopts an anti-parallel double-strand intertwined β5.6helical conformation with 30° orientation with respect to the normal with a thickness of 25Å. The interface between bulk water and the VGA monolayer was investigated by x-ray reflectivity as well as by comparing the experimental and the simulated PM-IRRAS spectra on D2O and H2O, which suggested the presence of oriented water molecules between the bulk and the monolayer.

X-ray reflectivity (XR) and diffraction at grazing angles of incidence (GID) were conducted to determine the structure of synthetic D-erythro C18-ceramide films at the air-water interface at various surface pressures (π). Analysis of the GID reveals that the monomolecular film, at the crystalline phase (π>0mN/m), is predominantly hexagonal. In this crystalline phase, the analysis of the reflectivity yields an electron density profile that consists of three distinct homogeneous slabs, one associated with the headgroup region and the other two with the hydrocarbon chains. At large molecular areas (π ≈ 0), isolated crystalline domains coexist with two-dimensional gas phase. Within the crystalline domains, we find an orthorhombic arrangement of the chains that coexists with the hexagonal symmetry. It is argued that the two-dimensional orthorhombic crystals are induced by hydrogen bonding between headgroups even at very low surface pressures. Although their structure is incommensurate with the simple hexagonal arrangement, they act as nucleation centers for the conventional hexagonal phase which dominates at high π.

We report on the assembly of gold nanoparticle (AuNPs) superlattices at the liquid/vapor interface and in the bulk of their suspensions. Interparticle distances in the assemblies are achieved on multiple length scales by varying chain lengths of surface grafted AuNPs by polyethylene glycol (PEG) with molecular weights in the range 2000–40,000 Da. Crystal structures and lattice constants in both 2D and 3D assemblies are determined by synchrotron-based surface-sensitive and small-angle X-ray scattering. Assuming knowledge of grafting density, we show that experimentally determined interparticle distances are adequately modeled by spherical brushes close to the θ point (Flory–Huggins parameter, χ≈12) for 2D superlattices at a liquid interface and a nonsolvent (χ = ∞) for the 3D dry superlattices.