•Composite microcapsules were formed by encapsulating primary microcapsules in calcium shellac matrix.•In primary microcapsules oil was encapsulated in melamine formaldehyde or CaCO3 nanoparticle walls.•The composite microcapsules showed enhanced mechanical strength and reduced oil leakage.•Calcium shellac could be an effective barrier to protect the primary microcapsules from rupture.A calcium shellac (CS) matrix was used to encapsulate polymeric melamine formaldehyde microcapsules (A) or CaCO3 nanoparticles-stabilized microcapsules (B), both of which encapsulated an oil-based active ingredient, producing A–CS or B–CS composite microcapsules. The mechanical properties and oil release profiles of the composite microcapsules were evaluated. The composite microcapsules showed enhanced mechanical stability and reduced leakage of the active ingredient by one order of magnitude.

•Double-shell composite microcapsules were synthesized.•Mechanical property and leakiness of the microcapsules were characterized.•SEM, TEM, GC and micromanipulation techniques were employed.•The strength and leakiness of the microcapsules could be engineered separately.Double-shell composite microcapsule with a ripened CaCO3 nanoparticle outer shell and melamine formaldehyde (MF)/copolymer inner shell shows advantages in adjustable permeability and mechanical strength, comparing with single shell microcapsules. Here, we have systematically studied the effects of certain formulation parameters on the properties of the double-shell composite microcapsules, i.e. the MF cross-linking time and the concentration of the aqueous CaCl2 and Na2CO3 used for the ripening process of CaCO3 nanoparticles. The properties of the microcapsules such as average diameter, wall thickness, degree of wall formation formed by the ripened CaCO3 nanoparticles, nominal rupture stress and leakiness were characterized.Figure optionsDownload full-size imageDownload as PowerPoint slide

Here we present novel double shell composite microcapsules (melamine formaldehyde (MF) polymer inner shell and ripened CaCO3 nanoparticle outer shell) prepared using a method based on in situ polymerisation to form a MF polymer shell inside the ripened CaCO3 nanoparticulate microcapsules wall.

Poly(1-methylpyrrol-2-yl)squaraine (PMPS) particles have been characterised using SEM. The PMPS particles were used as templates to prepare bare silica and iron–silica hollow spheres, which were characterised using TEM and SEM. The PMPS particles and the hollow spheres are not uniformly sized and are agglomerated. The hollow spheres with larger diameters (>900 nm) contain an internal ‘Russian doll’ structure. The iron–silica hollow spheres are fused to one another, and the hollow spheres have a heterogeneous wall thickness. The silica and iron–silica hollow spheres both aggregate by size. There are two different size populations (for the diameter) of the bare silica and iron–silica hollow spheres. The smaller silica spheres have thinner walls compared to the larger silica hollow spheres. The larger silica hollow spheres and the iron–silica hollow spheres have similar wall thicknesses. The iron compound in the iron–silica hollow spheres has an oxidation state of 3+ and is crystalline.

In the research reported here, an in situpolymerization process has been used to produce melamine formaldehyde microcapsules containing an oil-based industrial precursor. Here the microcapsules were produced with a low formaldehyde to melamine molar ratio (0.20–0.49) compared to previous literature reports (2.30–5.50). The properties of the microcapsules such as morphology, particle diameter and distribution, wall thickness, mechanical strength, and encapsulation efficiency were characterized, and it was found that the wall thickness and mechanical properties of microcapsules were modulated as a function of formaldehyde to melamine (F/M) molar ratio. The wall thickness of the microcapsules measured by transmission electron microscopy (TEM) increased from 80 ± 1.9 to 308 ± 1.7 nm (285 ± 2.4% increase) when the F/M molar ratio was increased from 0.20 to 0.49 (145% increase), and the nominal rupture stress of the microcapsules measured by a micromanipulation technique increased from 1.3 ± 0.1 to 4.2 ± 0.4 MPa (223 ± 11.5% increase). In contrast, when the F/M molar ratio increased from 0.49 to 2.30 (369%), the wall thickness of microcapsules only increased by 14 ± 0.8% and the nominal rupture stress of the microcapsules only increased by 66 ± 12.8%. Thus, it has been shown that significant reduction in the levels of formaldehyde content is possible from previous literature reports, whilst only marginally reducing the mechanical properties, and still maintaining the encapsulation efficiency of ∼75%.

Self-assembled monolayer (SAM) formation of silanes on SiO2 surfaces has been extensively studied. However, SAMs formed on silicon nitride (Si3N4) substrates have not been explored to the same level as SiO2, even though they are of technological interest with a view to the chemical modification of microelectromechanical systems (MEMS). Therefore, this article presents the formation and characterisation of 3-aminopropyltrimethoxysilane (APTMS) SAMs on Si3N4 substrates from solution phase and vapour phase, compared to the well characterised APTMS SAMs formed on SiO2 surfaces. Contact angle, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and ellipsometric data indicate the formation of APTMS SAMs (0.55 nm ellipsometric thickness) after 60 min immersion of either SiO2 or Si3N4 substrates in APTMS solution (0.5 mM in EtOH). By comparison Si3N4 substrates exposed to APTMS vapour, at 168 mbar for 60 min, result in the formation of the equivalent of a bi or trilayer of APTMS.

The chemical modification caused by prolonged exposure to X-rays on a series of para-substituted phenyl moieties (−NO2, −CN, −CHO, −COOH, −CO2Me, and −CO2tBu) at the surface of thiolate-Au self-assembled monolayers (SAMs) has been investigated by X-ray photoelectron spectroscopy (XPS). Furthermore, the influence that the phenyl group has on the chemical modification induced by the X-ray irradiation on the SAMs was investigated by comparing the XPS results obtained from irradiation on a NO2-aromatic-terminated SAM (6-(4-nitro-phenoxy)-hexane-1-thiolate (NPHT)) and NO2-aliphatic-terminated SAM (thioacetic acid S-(12-nitrododecyl) ester (TNDDE)). The NPHT and TNDDE SAMs have been shown to behave differently to X-ray exposure. The irradiation of the NPHT SAM led to the reduction of the nitro (−NO2) moiety to the amine (−NH2) moiety, as shown by the decrease in the intensity of the N 1s photoelectron peak for −NO2 (406 eV) in the XPS spectra with the concomitant increase in the N 1s photoelectron peak for −NH2 (399 eV). On the TNDDE SAM, XPS showed the −NO2 photoelectron peak again decreasing with prolonged X-ray irradiation whereas no peak was observed at 399 eV; therefore, the −NO2 moieties are selectively cleaved. No change was observed on the other functionalized monolayers apart from the −CO2tBu-functionalized monolayer, where after 100 min of X-ray irradiation approximately 11% of the carbon content was lost. The S 2p and O 1s spectra remained unchanged during the irradiation suggesting the conversion of the −CO2tBu to the −COOH moiety, although the conversion was not complete because the tertiary butyl moiety contributes 25% to the total carbon content of the SAM. Also, there was no evidence of the molecules desorbing from the substrate for any of the SAMs studied during the X-ray irradiation as shown by no change in the S 2p and C 1s XPS spectra taken during the X-ray irradiation.

The hydrolysis of methyl ester (–CO2Me) and tert-butyl ester (–CO2tBu) functionalized SAMs as a function of subphase temperature and pH is described. Contact angle measurements show that the methyl ester functionalized monolayer does not hydrolyse in pH 1–13 aqueous solutions heated up to 80 °C. In contrast, the –CO2tBu functionalized monolayer hydrolysed below pH 5. The rate and the extent of the hydrolysis were dependent on the temperature and pH of the aqueous solution. Using the Cassie equation, the activation energy for the hydrolysis of CO2tBu-phenyl functionalized SAM was determined as 75 ± 7 kJ mol−1 from the contact angle measurements. Furthermore, the adhesion properties of –CO2tBu and –COOH functionalized SAMs were investigated by depositing –NR2 and –COOH functionalized polystyrene nanoparticles onto the surfaces at pH 3 and 9. By AFM, it was observed that the particles bind preferentially to the –COOH functionalized SAM and the adhesion was pH dependent, with the largest coverage being observed at pH 3. Using the acquired understanding of the hydrolysis of –CO2tBu functionalized SAM and the particle adhesion properties, a simple and facile approach towards fabricating a particle density gradient on this surface is demonstrated. An acid gradient SAM (20 mm long) was prepared by mounting one end of a –CO2tBu functionalized SAM onto the hot side of a Peltier element (80 °C) in pH 1 aqueous solution. The substrate was subsequently immersed into a colloidal solution of –NR2 functionalized polystyrene nanoparticles, removed and rinsed. By AFM, the particle density was shown to be dependent on the surface coverage of –COOH moieties of the underlying SAM. The density started at 104 particles µm−2 on the hydrolysed end down to 0 particles µm−2 on the non-hydrolysed end.

Two series of hexakis(alkyloxy)triphenylenes have been synthesised and characterised. All materials contain two different lengths of n-alkyloxy chains. Series I (C5Cn) materials contain three –OC5H11 chains and three –OCnH2n + 1 chains. Series II (CmCn) materials contain three –OCmH2m + 1 chains and three –OCnH2n + 1 chains, such that m + n  = 10. Hexagonal columnar mesophases are observed in Series I for n ≥ 3 and, in Series II, for C5C5 and C6C4. Investigation by XRD shows that, within Series I, increasing the Cn chain length increases the intercolumnar spacing. Furthermore, the intercolumnar spacings for constitutional isomers are identical. The difference in the lengths of the two types of alkyl chain at the periphery of the molecules is defined as the Interdigitation Length (IL) and is a measure of the maximum extent of interdigitation that is possible between neighbouring molecules. Series I and II materials have been studied to probe the effect of IL on the change in enthalpy (ΔHCol–I) and entropy (ΔSCol–I) for the mesophase to isotropic liquid phase transition. In contrast to CxCx materials, which show a decrease in ΔHCol–I and ΔSCol–I with increasing chain length, Series I and II mesogens all exhibit ΔHCol–I and ΔSCol–I values similar to those of long chain CxCx materials, irrespective of chain length.

The synthesis of 13 discotic mesogens is described in which the well-known hexakis(pentyloxy)triphenylene liquid crystalline material has been chemically modified to incorporate one, two, three and six carbazole moieties. These modifications have been achieved by the alkylation or esterification of mono-, di-, tri- and hexa-hydroxytriphenylene derivatives with alkyl bromides and carboxylic acids incorporating the carbazole moiety. The pure compounds are not liquid crystalline in nature but when doped with TNF, hexagonal columnar mesophases are induced, as shown by DSC, OPM and X-ray diffraction. These mesophases exist below room temperature. The mesophase clearing temperatures are dependent on several factors including the chain length separating the carbazole moiety from the triphenylene core, and the nature of the ether or ester linkage, and the degree of TNF doping. The data suggest that the most stable mesophases (highest clearing temperatures) are formed when a 2 ∶ 1 complex is formed between the carbazole derivatives and the TNF, respectively. The correlation length obtained from X-ray diffraction reveals that the columnar order for one of the ether derivatives decreases, whereas the correlation length increases for one of the ester derivatives. This result suggests that the TNF is not only partaking in π–π noncovalent bonding interactions, but also in polar interactions with the CO bond. Such mesogenic carbazole derivatives may have advantageous photorefractive properties over the amorphous polymeric materials.

In the research reported here, an in situpolymerization process has been used to produce melamine formaldehyde microcapsules containing an oil-based industrial precursor. Here the microcapsules were produced with a low formaldehyde to melamine molar ratio (0.20–0.49) compared to previous literature reports (2.30–5.50). The properties of the microcapsules such as morphology, particle diameter and distribution, wall thickness, mechanical strength, and encapsulation efficiency were characterized, and it was found that the wall thickness and mechanical properties of microcapsules were modulated as a function of formaldehyde to melamine (F/M) molar ratio. The wall thickness of the microcapsules measured by transmission electron microscopy (TEM) increased from 80 ± 1.9 to 308 ± 1.7 nm (285 ± 2.4% increase) when the F/M molar ratio was increased from 0.20 to 0.49 (145% increase), and the nominal rupture stress of the microcapsules measured by a micromanipulation technique increased from 1.3 ± 0.1 to 4.2 ± 0.4 MPa (223 ± 11.5% increase). In contrast, when the F/M molar ratio increased from 0.49 to 2.30 (369%), the wall thickness of microcapsules only increased by 14 ± 0.8% and the nominal rupture stress of the microcapsules only increased by 66 ± 12.8%. Thus, it has been shown that significant reduction in the levels of formaldehyde content is possible from previous literature reports, whilst only marginally reducing the mechanical properties, and still maintaining the encapsulation efficiency of ∼75%.

Here we present novel double shell composite microcapsules (melamine formaldehyde (MF) polymer inner shell and ripened CaCO3 nanoparticle outer shell) prepared using a method based on in situ polymerisation to form a MF polymer shell inside the ripened CaCO3 nanoparticulate microcapsules wall.

The hydrolysis of methyl ester (–CO2Me) and tert-butyl ester (–CO2tBu) functionalized SAMs as a function of subphase temperature and pH is described. Contact angle measurements show that the methyl ester functionalized monolayer does not hydrolyse in pH 1–13 aqueous solutions heated up to 80 °C. In contrast, the –CO2tBu functionalized monolayer hydrolysed below pH 5. The rate and the extent of the hydrolysis were dependent on the temperature and pH of the aqueous solution. Using the Cassie equation, the activation energy for the hydrolysis of CO2tBu-phenyl functionalized SAM was determined as 75 ± 7 kJ mol−1 from the contact angle measurements. Furthermore, the adhesion properties of –CO2tBu and –COOH functionalized SAMs were investigated by depositing –NR2 and –COOH functionalized polystyrene nanoparticles onto the surfaces at pH 3 and 9. By AFM, it was observed that the particles bind preferentially to the –COOH functionalized SAM and the adhesion was pH dependent, with the largest coverage being observed at pH 3. Using the acquired understanding of the hydrolysis of –CO2tBu functionalized SAM and the particle adhesion properties, a simple and facile approach towards fabricating a particle density gradient on this surface is demonstrated. An acid gradient SAM (20 mm long) was prepared by mounting one end of a –CO2tBu functionalized SAM onto the hot side of a Peltier element (80 °C) in pH 1 aqueous solution. The substrate was subsequently immersed into a colloidal solution of –NR2 functionalized polystyrene nanoparticles, removed and rinsed. By AFM, the particle density was shown to be dependent on the surface coverage of –COOH moieties of the underlying SAM. The density started at 104 particles µm−2 on the hydrolysed end down to 0 particles µm−2 on the non-hydrolysed end.