15 research outputs found
Fractal Structure Evolution during Cement Hydration by Differential Scanning Calorimetry: Effect of Organic Additives
Low-temperature
differential scanning calorimetry (LT-DSC) is used to investigate
the microstructure of tricalcium silicate pastes, hydrating in pure
water and in the presence of comb-shaped polycarboxylate ether superplasticizers.
LT-DSC is shown to be a powerful technique, able to provide important
information on the porosity and on the fractality of the porous evolving
matrices by means of rapid and nondestructive measurements. In particular,
LT-DSC gives a semiquantitative estimation of the evolving porosity
(capillary, small gel, and large gel pores), the depercolation threshold
of the capillary pores, and the fractal dimension associated with
the probed porosity. The results are in good agreement with those
obtained by small-angle scattering methods ensuring that this approach,
based on the well-established and easily accessible DSC technique,
can provide valuable information on the evolving porosity and the
fractal nature of hydrating cement pastes
Nanostructured Surfactant-Based Systems for the Removal of Polymers from Wall Paintings: A Small-Angle Neutron Scattering Study
Nanostructured soft matter systems represent effective
and long-lasting
solutions with respect to traditional and often obsolete methodologies
for the conservation of works of art. In particular, complex fluids
such as micelles and microemulsions are the most performing media
for the removal of organic
materials from porous supports, like wall paintings or stones. In
this Article, we report on the characterization of two systems, EAPC
and XYL, which have shown good to optimal performances in the removal
of organic polymers from wall paintings. EAPC is a five-components
fluid composed of water, sodium dodecylsulfate (SDS), 1-pentanol (PeOH),
propylene carbonate (PC), and ethyl acetate (EA), while XYL is a âclassicalâ
o/w microemulsion, where <i>p</i>-xylene droplets are stabilized
in water by SDS and PeOH. Small-angle neutron scattering (SANS) with
contrast variation is used to infer a detailed picture of the structure
of these complex fluids, with a particular focus on the partition
of the components between the bulk phase and the nanocompartments.
We found that, differently from XYL, the EAPC system is neither a
microemulsion nor a simple micellar solution, with the cosolvents
partitioned between the dispersing phase and the disperse droplets.
These different structural features play a key role in defining the
cleaning effectiveness and specifically the kinetics of interaction
between the nanofluid and the polymeric coating to be removed, which
is of paramount importance for the application in the field. Both
of these nanofluids are effective in polymer removal, but EAPC is
considerably more efficient and versatile. The composition and the
structure at the nanoscale determine the capability of removing a
broad range of different polymer coatings from porous materials. A
representative case study is here described, addressing a particularly
challenging conservative issue, which is the removal of a multilayered
aged coating that was irreversibly damaging the pictorial layer of
the Annunciation Basilica in Nazareth
Multifunctional Magnetoliposomes for Sequential Controlled Release
The
simultaneous or sequential delivery of multiple therapeutic
active principles to a specific target is one of the main challenges
of nanomedicine. This goal requires the construction of complex devices
often extremely time and cost consuming. Supramolecular self-assemblies,
with building blocks of different nature, each providing a specific
function to the final construct, can combine a facile synthetic route
with a high tunability and structural control. In this study we provide
the proof-of-principle of a drug delivery system, DDS, constituted
of (i) liposomes, providing a fully biocompatible lipid scaffold suitable
to host both hydrophobic and hydrophilic drugs; (ii) a double-stranded
DNA conjugated with a cholesteryl unit that spontaneously inserts
into the lipid membrane; and (iii) hydrophobic and hydrophilic superparamagnetic
iron oxide nanoparticles (SPIONs) embedded inside the lipid membrane
of liposomes or connected to the DNA, respectively. Upon application
of an alternating magnetic field, the SPIONs can trigger, through
thermal activation, the release of a DNA strand or of the liposomal
payload, depending on the frequency and the application time of the
field, as proved by both steady-state and time-resolved fluorescence
studies. This feature is due to the different localization of the
two kinds of SPIONS within the construct and demonstrates the feasibility
of a multifunctional DDS, built up from self-assembly of biocompatible
building blocks
Tricalcium Silicate Hydration Reaction in the Presence of Comb-Shaped Superplasticizers: Boundary Nucleation and Growth Model Applied to Polymer-Modified Pastes
The Boundary Nucleation and Growth Model (BNGM), developed
for
the analysis of the hydration reaction of tricalcium silicate, has
been applied to study the kinetic behavior of pastes containing chemical
admixtures. Four comb-shaped polycarboxylate ether (PCE) superplasticizers
with well-known molecular structures have been added to tricalcium
silicate. The BNGM analysis performed on this series of additives
allows insights into the effect of the molecular architecture of the
PCEs on the induction time and rate constants. The results show that
decreasing the length of the polyethylene oxide side chains of the
PCE molecules increases the induction time. Also, the side chain density,
which highly influences the adsorption of the polymer to the C<sub>3</sub>S unreacted grains, is shown to significantly affect the duration
of the induction period: in particular, molecules with low side chain
density delay the setting of the paste to a greater extent than molecules
with denser side chains. Moreover, the chemical admixtures influence
the rate constants of the nucleation and growth processes, both reducing
them and affecting their temperature dependence
Hofmeister Phenomena in Nonaqueous Media: The Solubility of Electrolytes in Ethylene Carbonate
The solubility of some potassium salts (KF, KCl, KBr,
KI, KNO<sub>3</sub>, KClO<sub>4</sub>, KSCN, and KSeCN) in ethylene
carbonate
(EC) was determined at different temperatures with an inductively
coupled plasma atomic emission spectrometer. From the solubility measurements,
the thermodynamic parameters Î<i>G</i>, Î<i>H</i>, and Î<i>S</i>, of solution and of solvation,
were calculated. Measurements were carried out via XRD, ATR, and FTIR
to determine the effect of each salt on the properties of the solvent.
The open question of whether specific ion (Hofmeister) effects are
restricted to hydration peculiar to water is resolved. As for water,
the effects are due to solute (ion, dipolar) induced solvent structure
not accounted for by electrostatic forces. Cooperative quantum mechanical
forces are necessary to understand the phenomena
Magnetically Triggered Release From Giant Unilamellar Vesicles: Visualization By Means Of Confocal Microscopy
Magnetically triggered release from magnetic giant unilamellar vesicles (GUVs) loaded with Alexa fluorescent dye was studied by means of confocal laser scanning microscopy (CLSM) under a low-frequency alternating magnetic field (LF-AMF). Core/shell cobalt ferrite nanoparticles coated with rhodamine B isothiocyanate (MP@SiO<sub>2</sub>(RITC)) were prepared and adsorbed on the GUV membrane. The MP@SiO<sub>2</sub>(RITC) location and distribution on giant lipid vesicles were determined by 3D-CLSM projections, and their effect on the release properties and GUV permeability under a LF-AMF was investigated by CLSM time-resolved experiments. We show that the mechanism of release of the fluorescent dye during the LF-AMF exposure is induced by magnetic nanoparticle energy and mechanical vibration, which promote the perturbation of the GUV membrane without its collapse
State of Water in Hydrating Tricalcium Silicate Pastes: The Effect of a Cellulose Ether
Time-dependent quasi-elastic neutron
scattering (QENS) and differential
scanning calorimetry (DSC) were applied to study water dynamics and
hydration kinetic of the hydration reaction of tricalcium silicate
in the presence of a methyl hydroxyethyl cellulose (MHEC) additive.
The translational dynamics of the water confined in the developing
hydrated calcium silicate matrix was probed at the molecular scale
by QENS during the first 4 days, while the evolution of the matrix
porosity and the hydration kinetics were determined up to 28 days
of hydration by differential scanning calorimetry. The application
of the boundary nucleation and growth model consistently improved
the hydration kinetics picture, usually obtained from the application
of the classical Avrami-Eroveâev model, allowing the evaluation
of the individual contributions of nucleation and growth over the
entire hydration process. In the presence of the cellulose ether the
nature of the nucleation process is strongly modified, approaching
a âspatially randomâ hydration mechanism. The water
contained in the nanometric porosity of the hydrated calcium silicate
matrix, which is fundamental for the efficiency of the hydration process,
results increased when MHEC is added, leading to a delay of the onset
of the hydration process and the enhancement of the efficiency of
the reaction
Pore Size Effect on Methane Adsorption in Mesoporous Silica Materials Studied by Small-Angle Neutron Scattering
Methane adsorption in model mesoporous
silica materials with the
size range characteristic of shale is studied by small-angle neutron
scattering (SANS). Size effect on the temperature-dependent gas adsorption
at methane pressure about 100 kPa is investigated by SANS using MCM-41
and SBA-15 as adsorbents. Above the gasâliquid condensation
temperature, the thickness of the adsorption layer is found to be
roughly constant as a function of the temperature. Moreover, the gas
adsorption properties, such as the adsorbed layer thickness and the
specific amount of adsorbed gas, have little dependence on the pore
size being studied, i.e., pore radius of 16.5 and 34.1 Ă
, but
are mainly affected by the roughness of the pore surfaces. Hence,
the surface properties of the pore wall are more dominant than the
pore size in determining the methane gas adsorption of pores at the
nanometer size range. Not surprisingly, the gasâliquid condensation
temperature is observed to be sensitive to pore size and shifts to
higher temperature when the pore size is smaller. Below the gasâliquid
condensation temperature, even though the majority of gas adsorption
experiments/simulations have assumed the density of confined liquid
to be the same as the bulk density, the measured methane mass density
in our samples is found to be appreciably smaller than the bulk methane
density regardless of the pore sizes studied here. The mass density
of liquid/solid methane in pores with different sizes shows different
temperature dependence below the condensation temperature. With decreasing
temperature, the methane density in larger pores (SBA-15) abruptly
increases at approximately 65 K and then plateaus. In contrast, the
density in smaller pores (MCM-41) monotonically increases with decreasing
temperature before reaching a plateau at approximately 30 K
Probing the Cleaning of Polymeric Coatings by Nanostructured Fluids: A QCMâD Study
Complex fluids composed
of water, an organic solvent, and a surfactant
have been recently employed as cleaning systems to remove hydrophobic
materials, such as polymeric coatings, from solid surfaces. The simultaneous
presence of surfactants and an organic solvent with good affinity
for the polymer was proven necessary for the polymerâs removal,
but the comprehension of the cleaning mechanism is poorly understood.
In this Article, we investigated the mechanism of removal, highlighting
the specific role of each component in the interaction with the polymer
film. In particular, the results from quartz crystal microbalance
with dissipation monitoring (QCM-D) were compared with those obtained
by using confocal microscopy to follow in situ the effect of a nanostructured
fluid, i.e., a ternary formulation containing water, 2-butanone (MEK)
as a good solvent for the polymer, and a nonionic surfactant (C<sub>9â11</sub> ethoxylated alcohol, BR) on acrylic copolymer films
(Paraloid B72). The results indicate a two-step process: (i) the penetration
of the good solvent across the film causes the swelling of the polymer,
the weakening of polymerâpolymer interactions, and an increase
of molecular mobility, followed by (ii) the slow adsorption of amphiphilic
aggregates promoting the film detachment from the solid substrate.
A different behavior is observed in the presence of similar formulations
containing an anionic surfactant (sodium dodecyl sulfate, SDS), where
the adsorption of SDS micelles on the surface of the polymeric film
hinders solvent access into the polymer layer, rather than promoting
its detachment from the solid substrate
Complex Fluids Confined into Semi-interpenetrated Chemical Hydrogels for the Cleaning of Classic Art: A Rheological and SAXS Study
The
removal of aged varnishes from the surface of easel paintings
using the common conservation practice (i.e., by means of organic
solvents) often causes pigment leaching, paint loss, and varnish redeposition.
Recently, we proposed an innovative cleaning system based on semi-interpenetrated
polymer networks (SIPNs), where a covalently cross-linked polyÂ(hydroxyethyl
methacrylate), pHEMA, network is interpenetrated by linear chains
of polyÂ(vinylpyrrolidone), PVP. This chemical gel, simply loaded with
water, was designed to safely remove surface dirt from water-sensitive
artifacts. Here, we modified the SIPN to confine complex cleaning
fluids, able to remove aged varnishes. These complex fluids are 5-component
water-based nanostructured systems, where organic solvents are partially
dispersed as nanosized droplets in a continuous aqueous phase, using
surfactants. The rheological behavior of the SIPN and the nanostructure
of the fluids loaded into the gel were investigated, and the mechanical
behavior of the gel was optimized by varying both the cross-linking
density and the polymer concentration. Once loaded with the complex
fluids, the hydrogels maintained their structural and mechanical features,
while the complex fluids showed a decrease in the size of the dispersed
solvent droplets. Two challenging case studies have been selected
to evaluate the applicability of the SIPN hydrogels loaded with the
complex fluids. The first case study concerns the removal of a surface
layer composed by an aged brown resinous patina from a wood panel,
the second case study concerns the removal of a homogeneous layer
of yellowed varnish from a watercolor on paper. The results show that
the confinement of complex fluids into gels allowed unprecedented
removal of varnishes from artifacts overcoming the limitations of
traditional cleaning methods