Formation of 2D-networked structures of disk-like islands for ultrathin Langmuir–Schaefer (LS) films of thiol-coated Au-nanoparticles (DT-AuNPs) on H-passivated Si substrates is evidenced for the ...first time, directly from a broad peak in grazing incidence small angle X-ray scattering data and also from atomic force microscopy images. Theoretical modeling of the system, carried out based on density–density and height–height correlation functions, supports well the formation of such structures. The structural information of the LS films, obtained at different surface pressure, helps to infer the growth of Langmuir monolayers of DT-AuNPs, which is very important in understanding the self-assembly process of nanoparticles at the air–water interface and in controlling the growth of 2D-networked nanostructures in large areas. On the surface of water, DT-AuNPs first self-assembled around different points to form disk-like islands of nanometer size and monolayer height, due to the complex balance of long range van der Waals attractions and short-range steric repulsion of the DT-AuNPs, initiated by solvent evaporation and also to optimize the hydrophobic repulsive force of water. On barrier compression, the size and 2D-network of the islands grow due to a combined effect of collision induced coalescence and solid-like behavior resisting deformation of the islands. On the other hand, the separation between the DT-AuNPs either decreases or increases depending upon the competitive effects of packing or buckling.
We have demonstrated that chitosan has strong affinity with fatty acid (stearic acid) and adsorbs at the fatty acid monolayer at air–water interface, despite its lack of surface activity. Chitosan ...insertion caused an expansion of chitosan-fatty acid mixed monolayers and reduced the elasticity and made the film heterogeneous. Chitosan endorses a local distortion of the fatty acid tails involving electrostatic, dipolar and hydrophobic interactions. The results could be rationalized in terms of a model in which at low surface pressure chitosan is situated at interface, interacting with stearic acid molecules via electrostatic and hydrophobic interactions whereas at high pressure chitosan mainly located at subsurface beneath stearic acid molecules. In the latter case the interaction is predominantly electrostatic yielding very small contribution to the surface pressure. Reduction of temperature allows more number of chitosan molecules to reach surface. In addition, chitosan could be transferred onto solid supports employing LB technique by mixing with fatty acid.
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•Chitosan-fatty acid interactions at air–water interface.•Interactions modification by chitosan mole fraction and temperature.•Relocation of chitosan on solid substrate employing Langmuir-Blodgett technique via mixing with fatty acid.•Surface pressure induced 2D to 3D structural transition of chitosan-fatty LB films.
The interaction of chitosan with bio-membranes, which plays important role in deciding its use in biological applications, is realized by investigating the interaction of chitosan with stearic acid (fatty acid) in Langmuir monolayers (at air–water interface) and Langmuir-Blodgett (LB) films (after transferring it onto solid substrate). It is found from the pressure-area isotherms that the chitosan insertion causes an expansion of chitosan-fatty acid hybrid monolayers, which reduces the elasticity and make the film heterogeneous. It is likely that at low surface pressure chitosan is situated at the interface, interacting with stearic acid molecules via electrostatic and hydrophobic interactions whereas at high pressure chitosan mainly located at subsurface beneath stearic acid molecules. In the latter case the interaction is predominantly electrostatic yielding very small contribution to the surface pressure. The reduction of temperature of the subphase water allows more number of chitosan molecules to reach surface to increase the pressure/interaction. On the other hand, although pure chitosan is found difficult to relocate on the substrate from air-water interface due to its hydrophilic-like nature, it alongside stearic acid (amphiphilic molecules) can be transferred onto substrate using LB technique as evident from infrared spectra. Their out-of-plane and in-plane structures, as extracted from two complementary surface sensitive techniques- X-ray reflectivity and atomic force microscopy, are found strongly dependent on the chitosan mole fraction and the deposition pressure. These analysis of the film-structure will essentially allow one to model the system better and provide better insight into the interaction.
Structures of Langmuir-Schaefer (LS) monolayers of thiol-coated Au-nanoparticles (DT-AuNPs) deposited on H-terminated and OTS self-assembled Si substrates (of different hydrophobic strength and ...stability) and their evolution with time under ambient conditions, which plays an important role for their practical use as 2D-nanostructures over large areas, were investigated using the X-ray reflectivity technique. The strong effect of substrate surface energy (
γ
) on the initial structures and the competitive role of room temperature thermal energy (
kT
) and the change in interfacial energy (Δ
γ
) at ambient conditions on the evolution and final structures of the DT-AuNP LS monolayers are evident. The strong-hydrophobic OTS-Si substrate, during transfer, seems to induce strong attraction towards hydrophobic DT-AuNPs on hydrophilic (repulsive) water to form vertically compact partially covered (with voids) monolayer structures (of perfect monolayer thickness) at low pressure and nearly covered buckled monolayer structures (of enhanced monolayer thickness) at high pressure. After transfer, the small
kT
-energy (in absence of repulsive water) probably fluctuates the DT-AuNPs to form vertically expanded monolayer structures, through systematic exponential growth with time. The effect is prominent for the film deposited at low pressure, where the initial film-coverage and film-thickness are low. On the other hand, the weak-hydrophobic H-Si substrate, during transfer, appears to induce optimum attraction towards DT-AuNPs to better mimic the Langmuir monolayer structures on it. After transfer, the change in the substrate surface nature, from weak-hydrophobic to weak-hydrophilic with time (
i.e.
Δ
γ
-energy, apart from the
kT
-energy), enhances the size of the voids and weakens the monolayer/bilayer structure to form a similar expanded monolayer structure, the thickness of which is probably optimized by the available thermal energy.
Substrate surface energy (
γ
) controls the initial structures of Langmuir-Schaefer monolayers of Au-nanoparticles, while the competitive room temperature thermal energy (
kT
) and the change in interfacial energy (Δ
γ
) decide their time evolution under ambient conditions.
Effect of dimethyl sulfoxide (DMSO) doping on poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) thin films have been optimized for obtaining better hole transport layer in hybrid ...solar cell. The correlation between morphology and conductivity is established through atomic force microscopy and transmission length method measurements. On the other hand, change in the shape of the building blocks (from spheroidal-like to ellipsoidal-like) in the PEDOT:PSS films with DMSO concentration is apparent from their electron density profiles and topographies, suggesting possible conformational change (from coil-like to rod-like) in film by X-ray reflectivity. Such change is further evident from their compositional profiles, work functions and electronic band structures estimated from X-ray and ultraviolet photoelectron spectroscopies. In fact, complementary information suggest that near 5% DMSO doped PEDOT:PSS film is governed through maximum in-plane extended ellipsoidal-like blocks as well as well-organized in out-of-plane ordering which is likely to be the optimum structure for increased the highest electrical conductivity up to 1230 S/cm. Finally, maximum power conversion efficiency of 11% with open-circuit voltages around 600 mV, a short-circuit current density higher than 30 mA/cm2 and a fill factor of 59.4% is achieved for the 5% DMSO doped PEDOT:PSS/n-Si hybrid solar cell, which is perfectly correlated with their structure.
•PEDOT:PSS domains are maximum length in 5% DMSO.•In 5% DMSO, the thickness of PSS layer surrounded on PEDOT is minimum.•Interface dipole is strong in 5% DMSO.•Conductivity and PEC is maximum in 5% DMSO doped PEDOT:PSS thin film and solar cell device.
Structures of Langmuir-Schaefer (LS) monolayers of thiol-coated Au-nanoparticles (DT-AuNPs) deposited on H-terminated and OTS self-assembled Si substrates (of different hydrophobic strength and ...stability) and their evolution with time under ambient conditions, which plays an important role for their practical use as 2D-nanostructures over large areas, were investigated using the X-ray reflectivity technique. The strong effect of substrate surface energy (γ) on the initial structures and the competitive role of room temperature thermal energy (kT) and the change in interfacial energy (Δγ) at ambient conditions on the evolution and final structures of the DT-AuNP LS monolayers are evident. The strong-hydrophobic OTS-Si substrate, during transfer, seems to induce strong attraction towards hydrophobic DT-AuNPs on hydrophilic (repulsive) water to form vertically compact partially covered (with voids) monolayer structures (of perfect monolayer thickness) at low pressure and nearly covered buckled monolayer structures (of enhanced monolayer thickness) at high pressure. After transfer, the small kT-energy (in absence of repulsive water) probably fluctuates the DT-AuNPs to form vertically expanded monolayer structures, through systematic exponential growth with time. The effect is prominent for the film deposited at low pressure, where the initial film-coverage and film-thickness are low. On the other hand, the weak-hydrophobic H-Si substrate, during transfer, appears to induce optimum attraction towards DT-AuNPs to better mimic the Langmuir monolayer structures on it. After transfer, the change in the substrate surface nature, from weak-hydrophobic to weak-hydrophilic with time (i.e. Δγ-energy, apart from the kT-energy), enhances the size of the voids and weakens the monolayer/bilayer structure to form a similar expanded monolayer structure, the thickness of which is probably optimized by the available thermal energy.
The structural evolution of thiol-capped Au-nanoparticle (AuNP) multilayers on a H-passivated Si substrate, formed through a Langmuir-Schaefer (LS) deposition process, has been investigated using ...complementary grazing incidence X-ray scattering techniques. The fractional coverage multilayers of AuNPs, formed through a multi-transfer process, are found to be quite unstable under ambient conditions. The thickness of these decreases with time and tends to saturate toward a near unique thickness (NUT 6 nm). Although initial low coverage and their instability create hindrance in the control and formation of desired 3D-nanostructures in the bottom-up approach, the formation of a NUT-layer, through time-evolution, is quite distinctive, thus interesting. It is clear from the evolution that the thermodynamically driven monolayer structures (of AuNPs) at the air-water interface become thermodynamically unstable when transferred sequentially onto the solid substrate. The thermal energy (
kT
) and the partial change in the substrate surface energy (Δ
γ
) create the instability and induce diffusion in the AuNPs, which in the presence of a net attractive force towards the substrate (arising from anisotropic interaction of the top AuNPs with the other AuNPs and/or hydrophobic substrate) tries to create a thermodynamically favourable and relatively stable NUT-layer through reorganization for a different duration. This happens if the number of AuNPs is less than or equal to the maximum number that can be accommodated within the NUT. The value of the NUT mainly depends on the particle size and a
kT
-energy related fluctuation of particles. Furthermore, the formation of the NUT-layer indicates that the hydrophobic-hydrophobic interaction mediated net attraction towards the substrate is long range, while the hydrophilic-hydrophobic interaction mediated repulsion and/or
kT
-energy induced fluctuations are short range.
Formation of a near unique thickness layer of nanoparticles due to a long-range hydrophobic-hydrophobic interaction mediated net attraction toward a substrate, and a short-range hydrophilic-hydrophobic interaction mediated repulsion and/or thermal energy induced fluctuation.
Structural evolution of solution-aged poly(3-hexylthiophene) P3HT thin films during thermal annealing (TA) was studied using complementary
in situ
X-ray reflectivity (XR) and
ex situ
atomic force ...microscopy (AFM) and optical absorption (UV-Vis) techniques to understand the possibility of obtaining enhanced edge-on oriented (EO) ordering for better device properties. The presence of P3HT nanofibers (NFs), which were formed through π-π stacking within solution during aging, is evident in the films. Such NFs are well-organized near the film-substrate interface and less organized near the film-air interface due to the respective slow and fast evaporation rates of the solvent during spin-coating. Accordingly, prominent EO ordering (
i.e.
the electron density contrast between the polymer backbone and side chains is maximum, Δ
ρ
Δ
ρ
m
) near the substrate and negligible ordering (
i.e.
Δ
ρ
→ 0) near the top surface took place following the standard decay function: Δ
ρ
(
z
) = Δ
ρ
m
exp(−
z
/
ζ
), where the critical decay length,
ζ
, is the measure of the out-of-plane ordering. TA fails to improve the Δ
ρ
m
-value,
i.e.
the EO ordering near the substrate and also the total crystalline aggregates or NFs, rather deteriorates both, when annealed near the melting temperature of P3HT. TA improves the
ζ
-value,
i.e.
the EO ordering of the more out-of-plane region due to thermal energy induced alignment of the NFs; however, lack of improvement of the EO ordering near the substrate is of concern. A relatively low viscous polymer solution and low spin-coating speed play important roles in the formation of a smooth film-substrate interface and better EO ordering near that interface. Though solvent vapor annealing (SVA) fails to improve the structure, the combination of SVA and TA,
i.e.
SVTA, improves the in-plane EO ordering near the substrate (
i.e.
the Δ
ρ
m
-value) along with the out-of-plane ordering (
i.e.
the
ζ
-value) of the film. Such improvements, which are probably through the alignment and growth of NFs, promoted by SVTA induced proper diffusion, are of immense importance for obtaining better device properties.
In solution-aged thin films, edge-on oriented ordering of nanofibers, along the
z
-direction, extends by thermal annealing, while near the film-substrate interface, it improves by combined solvent vapor and thermal annealing
Correction for 'Growth of thiol-coated Au-nanoparticle Langmuir monolayers through a 2D-network of disk-like islands' by Mala Mukhopadhyay
et al.
,
RSC Adv.
, 2016,
6
, 12326-12336.
Formation of 2D-networked structures of disk-like islands for ultrathin Langmuir-Schaefer (LS) films of thiol-coated Au-nanoparticles (DT-AuNPs) on H-passivated Si substrates is evidenced for the ...first time, directly from a broad peak in grazing incidence small angle X-ray scattering data and also from atomic force microscopy images. Theoretical modeling of the system, carried out based on density-density and height-height correlation functions, supports well the formation of such structures. The structural information of the LS films, obtained at different surface pressure, helps to infer the growth of Langmuir monolayers of DT-AuNPs, which is very important in understanding the self-assembly process of nanoparticles at the air-water interface and in controlling the growth of 2D-networked nanostructures in large areas. On the surface of water, DT-AuNPs first self-assembled around different points to form disk-like islands of nanometer size and monolayer height, due to the complex balance of long range van der Waals attractions and short-range steric repulsion of the DT-AuNPs, initiated by solvent evaporation and also to optimize the hydrophobic repulsive force of water. On barrier compression, the size and 2D-network of the islands grow due to a combined effect of collision induced coalescence and solid-like behavior resisting deformation of the islands. On the other hand, the separation between the DT-AuNPs either decreases or increases depending upon the competitive effects of packing or buckling.
Formation of 2D-networked structures of disk-like islands for ultrathin Langmuir-Schaefer (LS) films of thiol-coated Au-nanoparticles (DT-AuNPs) on H-passivated Si substrates is evidenced for the first time, by X-ray scattering data and AFM images.
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