Laponite Gels Research Articles

Growth and static stability of bubble clouds in yield stress fluids

This study explores the growth and static stability of bubble clouds in yield-stress fluids using an experimental approach. Carbopol gels with varying concentrations and initial gas contents as well as Laponite gels are used as model yield stress fluids in our experiments. A vacuum system is exploited to generate the bubbles and control their growth in the gels. The focus of this study is on determining the maximum gas concentration which could be held trapped in the system and the critical yield number, i.e. the ratio of the yield stress to the buoyancy stress at the onset of motion. Our findings demonstrate the effect of the bubbles proximity as well as the gel structure and rheology on both the maximum gas concentration and critical yield number. Our results confirm that for higher gas fractions, the critical yield number is larger. Also, they show that the size and degree of elongation of the bubbles at the onset of motion are controlled by their proximity as well as the gel rheology. Moreover, our results reveal two different scenarios for the bubble release depending on the uniformity of the structure of the gel. In the case of low concentration Carbopol gels, characterized by uniform structures, quasi mono-dispersed bubble suspensions are formed. At a pretty high gas concentration, this might lead to a bubble cloud burst upon static instability onset. Conversely, in the case of high concentration Carbopol gels or Laponite gels, the polydisperse bubble suspensions emerge and the bubble release occurs gradually rather than suddenly. It can be associated with the heterogeneous structure of these gels stemming from their significant shear history dependence.

Time-dependent clay gels: Stepdown shear rate behavior, microstructure, ageing, and phase state ambiguity

To study the time-dependent properties of clay gels in the structural rejuvenation mode, a combination of the stepdown shear rate method and an ageing test is advocated. In this mode, the structural development process at two different initial equilibrium states during the low stepdown shear rate and the rest period of the ageing test were followed. The roles played by the electric double layer (EDL) repulsive force in this structural development process with and without shear, for platelet sodium montmorillonite or NaMnt, hectorite and Laponite gels, and fibrous sepiolite gels were assessed. The response of the stepdown shear stress and ageing yield stress reflects the action of these forces on the structural rejuvenation kinetics and the type of structure formed. The platelet clay gels with their strong EDL repulsive particle interaction commenced the structural development process immediately and formed an open network structure. This process is short in shear and takes years when without. The fibrous sepiolite gel with its weak EDL repulsive interaction did not display structural rejuvenation in shear and only showed a significant yield stress increase after the first few hours of ageing. An additional issue concerning the stability of the isotropic liquid (IL) phase state of dilute Laponite dispersions was addressed. These dispersions aged for >9 years, displaying that yield stress and network structure confirmed that the IL phase is unstable. A low energy path available for Laponite particles to aggregate was discussed. A new method for determining the flocculate phase state was also presented.

Ageing behaviour spanning months of NaMt, hectorite and Laponite gels: Surface forces and microstructure – A comprehensive analysis

Recent “artifact-free” microstructure information enabled the development of a more credible model for explaining the ageing time-dependent rheological behavior of NaMt, hectorite and Laponite gels. These gels displayed pronounced ageing behavior lasting months. The platelet morphology and the localised nature of the negative and positive charges produced the essential forces and interaction configurations to form the time-dependent structure. This structure is composed of nano-sized flexible platelets interacting both attractively to form the network junctions and repulsively to open up the structure. These junctions were formed by heterogeneous charge and van der Waals attractions between the jagged and curled edges, and the face of the interacting platelets. The force that is responsible for the time-dependent behaviour is the EDL repulsive force. This force governs the development of the 3-D network structure and drives it towards a minimum free energy state. This process takes a long time to complete. The resultant microstructure is completely interpenetrated with interconnected nanopores trapping as much as 99% of water in volume. At high ionic strength or 0.3 M KCl, the NaMt or bentonite gels became time independent as the van der Waals force formed the structure. The Leong model described the initial ageing behavior well. For the nanodiscotic Laponite gels, the 3-D structure is formed from sheets instead of primarily disks contradicting prevailing model. With the latest microstructure information, new mechanisms were proposed to account for the high yield stress at low solids, low permeability, intercalation behavior, layer stacking and enlarged dried platelets.

Injectable nanoclay gels for angiogenesis

The retention and sustained activity of therapeutic proteins at delivery sites are goals of regenerative medicine. Vascular endothelial growth factor (VEGF) has significant potential in promoting the growth and regeneration of blood vessels but is intrinsically labile. This is exacerbated by the inflammatory microenvironments at sites requiring regeneration. For VEGF to be efficacious, it may require a carrier that stabilises it, protects it from degradation and retains it at the site of interest. In this study, we tested the hypothesis that injectable nanoclay gels comprising Laponite™ XLG (a synthetic hectorite clay) can stabilise VEGF and retain it in the active form for therapeutic delivery. To achieve this, VEGF was incorporated in Laponite gels and its activity tested at a range of concentrations using in vitro cell culture tubulogenesis assays and in vivo angiogenesis assays. We found that VEGF-Laponite gels enhanced tubulogenesis in a dose-dependent manner in vitro. When administered subcutaneously in vivo, Laponite was retained at the injection site for up to a period of three weeks and promoted a 4-fold increase in blood vessel formation compared with that of alginate or vehicle controls as confirmed by CD31 staining. Notably, as compared to alginate, Laponite gels did not release VEGF, indicating a strong interaction between the growth factor and the nanoclay and suggesting that Laponite enhancement of VEGF efficacy is due to its retention at the implantation site for a prolonged period. Our approach provides a robust method for the delivery of bioactive recombinant VEGF without the necessity for complex hydrogel or protein engineering. Statement of significanceIn medicine, it is important to deliver drugs to a particular location in the body. Often, however, the drugs are quickly broken down and carried away in the blood before they can exert their effect. In this study, we used a type of synthetic clay, called Laponite™, to preserve a molecule, named VEGF, that stimulates the growth of blood vessels. Previously, we have been able to bind VEGF to the surface of clays, but the clay is not effective when injected or applied as a gel. Herein, we show that we can mix VEGF with the clay and that it strongly stimulates blood vessel growth. We speculate that this would be a useful material for skin wound healing.

Injectable Nanoclay Gels for Angiogenesis

The retention and sustained activity of therapeutic proteins at delivery sites are goals of regenerative medicine. Vascular endothelial growth factor (VEGF) has significant potential in promoting the growth and regeneration of blood vessels but is intrinsically labile. This is exacerbated by the inflammatory microenvironments at sites requiring regeneration. For VEGF to be efficacious it may require a carrier that stabilises it, protects it from degradation and retains it at a site of interest. In this study we tested the hypothesis that injectable nanoclay gels composed of Laponite XLGTM can stabilise VEGF and retain it in active form for therapeutic delivery. To achieve this, VEGF was incorporated in Laponite gels and its activity tested at a range of concentrations using in vitro cell culture tubulogenesis assays and in vivo angiogenesis assays. We found that VEGF-Laponite gels enhanced tubulogenesis in a dose-dependent manner in vitro. When administered subcutaneously in vivo Laponite was retained at an injection site for up to a period of three weeks and promoted a 4-fold increase in blood vessel formation compared with alginate or vehicle controls as confirmed by CD31 staining. Notably, in contrast to alginate, Laponite gels did not release VEGF, indicating a strong interaction between the growth factor and the nanoclay, and suggesting that Laponite enhancement of VEGF efficacy is due to its retention at an implantation site over a prolonged period. Our approach provides a robust method for delivery of bioactive recombinant VEGF without the necessity for complex hydrogel or protein engineering.

Effects of aging on the yielding behaviour of acid and salt induced Laponite gels

The synthetic clay Laponite, when dispersed in water, shows rich phase behaviour that depends on both clay and ionic concentrations. The flow properties of this clay dispersion can be tuned by incorporating different additives such as acid and salt. In this work, we use rheology to study the mechanical properties of Laponite gels when prepared by adding sulfuric acid (H2SO4) and common salt (NaCl). The acid induced Laponite gels form a visco-elastic solid with increasing idle time, while the salt induced Laponite gel transforms to a soft solid almost immediately after sample preparation. Furthermore, in the acid induced Laponite gels, a nonmonotonic evolution of yield stress with idle time is observed. No such observation is evident for the salt induced Laponite gels. These observations are connected to the underlying morphology of the sample which is governed by the osmotic pressure driven aging behaviour of the suspensions. We use cryogenic scanning electron microscopy images for a qualitative understanding of the gel morphologies which we relate to the acquired rheological data. The aging dynamics and the subsequent structural evolution of the sample are further verified by performing a UV–Vis spectroscopy study and found to be in agreement with the rheological and Cryo-SEM experiments.

Surface chemistry and rheology of Laponite dispersions — Zeta potential, yield stress, ageing, fractal dimension and pyrophosphate

The ageing behaviour of Laponite gels at the phase boundary of attractive gel and flocculated state (ionic strength~0.01M 1:1 electrolyte) was investigated due to a lack of study in this region. Zeta potential and yield stress measurement revealed that freshly prepared Laponite dispersion took time to reach the surface chemical equilibrium (SCE) state. The higher the ionic strength, the shorter was the time needed. This well-defined structural state was employed at the commencement of ageing study. The ageing behaviour was characterised by a rapidly increasing yield stress region followed by a gradually increasing region and then by a plateau region. Both the initial and fully aged yield stress of Laponite gels increased with ionic strength and solid loading. Both the Leong and the two-parameter logarithmic time models described the ageing behaviour quite well. The relationship between the yield stress at the SCE state and at the fully recovered or rejuvenated state, and volume fraction obeyed a power law model. The fractal dimension of the two states was the same 2.0. This study also investigated the yield stress-pH behaviour of Laponite gel with and without pyrophosphate additive. Pure Laponite dispersion displayed a maximum yield stress at high pH. A drop in yield stress occurred at low pH region and eventually approaching zero yield stress. A totally opposite trend was observed with pyrophosphate additive. No yield stress was detected at high pH region and a maximum yield stress was located at pH5 followed by a drop in yield stress until pH2. This drop in the yield stress regardless of the presence of pyrophosphate, was due to the particle agglomeration promoted by low pH.

Hierarchical self-assembly, relaxations and ergodic–non-ergodic transition in laponite ionogels

We report on the formation of entropic ionogels (gels in IL solutions) of laponite platelets in ionic liquid (IL), 1-ethyl-3-methyl imidazolium chloride, solutions at room temperature (0<[IL]<0.05% (w/v)). Self-assembled colloidal networks were formed following a growth mechanism given by, ηr∼(1−t/tgvis)−p for t<tgvis; and G0∼(t/tgrheo−1)β for t>tgrheo where ηr, G0 and tgvis,rheo represent relative viscosity, low frequency storage modulus and gelation time (determined from viscosity and rheology) respectively. The exponent p was found to increase from 0.23 to 0.85 with increase in IL concentration implying slower network growth kinetics, which helped in the formation of stronger ionogels (β decreased from 2.40 to 0.83). It was found that tgvis>tgrheo which indicated that the network, after formation, required considerable amount of equilibration time (longer for low IL concentration) to reorganize and attain a solid-like structure capable of sustaining shear deformation. Reorganization of clay platelets caused reduction in the inter platelet repulsion due the IL-double layer screening and facilitated formation of stronger ionogels for samples with [IL]≤0.03% (w/v). Dynamic structure factor data revealed two primary relaxation modes: (i) the anomalous slow mode that was frozen at all IL concentrations, and (ii) the diffusive fast mode that contained two diffusion components both strongly dependent on IL concentration. Neutron scattering data could be split into two distinct scattering regions: (i) 0.001<q<q# Å−1, I(q)∼q−α with α=0.97–1.67 (Power–law region) and (iii) q#<q<0.35Å−1, I(q)∼e−(q2Rc2/2) (Guinier–Porod region) with Rc=4.6–5.0Å−1. This implied existence of rod-like structures in homogeneous and rarefied clusters in fragile gels. In summary, it is shown that laponite gels could be systematically customized in IL solutions to generate a range of soft materials with properties solely dependent on IL concentration which may not exceed 0.05% (w/v).

Evolution of Self-organization and gelation in Laponite Ionogels

We report formation of colloidal gel network in aqueous laponite dispersions containing ionic liquid (IL). With the passage of time, these flowing dispersions reorganized and attained a solid-like rigid structure. Structural reorganization of clay platelets in the IL environment caused reduction in the inter platelet repulsion due the IL-double layer screening and facilitated formation of stronger ionogels for samples with [IL] 0.03% (w/v)). The structure factor comprised two relaxation modes diffusion fast mode followed by an anomalous slow mode. The slow mode was frozen at all IL concentrations whereas the fast mode contained two diffusion coefficients both strongly dependent on IL concentration. In summary, laponite gels could be systematically customized in IL solutions to generate a range of soft materials with properties solely dependent on IL concentration which may not exceed 0.05% (w/v).

Aging, Rejuvenation and Thixotropy in Complex Fluids: Time-dependence of the Viscosity at Rest and under Constant Shear Rate or Shear Stress

Abstract Complex fluids exhibit time-dependent changes in viscosity that have been ascribed to both thixotropy and aging. However, there is no consensus for which phenomenon is the origin of which changes. A novel thixotropic model is defined that incorporates aging. Conditions under which viscosity changes are due to thixotropy and aging are unambiguously defined. Viscosity changes in a complex fluid during a period of rest after destructuring exhibit a bifurcation at a critical volume fraction ϕc2. For volume fractions less than ϕc2 the viscosity remains finite in the limit t →∞. For volume fractions above critical the viscosity grows without limit, so aging occurs at rest. At constant shear rate there is no bifurcation, whereas under constant shear stress the model predicts a new bifurcation in the viscosity at a critical stress σB, identical to the yield stress σy observed under steady conditions. The divergence of the viscosity for σ≤σB is best defined as aging. However, for σ &gt; σB, where the viscosity remains finite, it seems preferable to use the concepts of restructuring and destructuring, rather than aging and rejuvenation. Nevertheless, when a stress σA(≤σB) is applied during aging, slower aging is predicted and discussed as true rejuvenation. Plastic behaviour is predicted under steady conditions when σ &gt; σB. The Herschel-Bulkley model fits the flow curve for stresses close to σB, whereas the Bingham model gives a better fit for σ &gt;&gt; σB. Finally, the model’s predictions are shown to be consistent with experimental data from the literature for the transient behaviour of laponite gels.

Analysis of Agarose, Carbopol, and Laponite Gel Poultices in Paper Conservation

Agarose, Carbopol, and Laponite gels were evaluated as alternatives to cellulose ether poultices for the local removal of moisture-sensitive adhesives on paper artifacts. These gels have noticeably different working properties than cellulose ethers, and are useful in a variety of paper conservation applications. The color stability of these materials was analyzed in dry powder form and as gel residues on paper. Analysis was performed by UV-visible spectroscopy, combined with visual examination under normal illumination and long-wave ultraviolet irradiation. Since earlier studies demonstrated that both Carbopol and Laponite contribute to the discoloration of paper after artificial aging, this study tested the effectiveness of a barrier tissue to block the deposition of residues on paper. Paper samples treated with Laponite were analyzed with a scanning electron microscope coupled with energy dispersive x-ray fluorescence spectroscopy to identify residues. Visual and ultraviolet examination techniques demonstrated that Carbopol (pH adjusted with sodium hydroxide) and Laponite caused discoloration on paper when applied directly, and that a barrier tissue was effective at blocking the deposition of residues. Agarose did not show adverse effects.

Scattering of Disklike Particle Suspensions: Evidence for Repulsive Interactions and Large Length Scale Structure from Static Light Scattering and Ultra-Small-Angle Neutron Scattering

We present static light scattering results for Laponite suspensions. Analyzing our data using the Zimm technique, we measure a second virial coefficient of 6.0 × 10-23 m3 at an ionic strength of 10-4 M. Both results agree well with recent theories and computations for the thermodynamics of hard disks. Our data support the conclusion that the classical Onsager result underestimates the repulsive contribution in discotic systems. We also present neutron scattering results at very low q which conclusively confirm the existence of large-scale structure in Laponite gels above the isotropic−nematic transition.

Microscale and Macroscale Diffusion of Water in Colloidal Gels. A Pulsed Field Gradient and NMR Imaging Investigation

Magnetic resonance imaging (MRI) has been used to determine quantitatively one-dimensional proton concentration profiles in clay gels prepared from water/heavy water mixtures, taking into account the variations of spin−spin relaxation rate and other effects on the signal intensity. The method has been used to determine the diffusion coefficient of water in Laponite gels at macroscale, by following the diffusion of water from a volume of gel prepared with water into a volume of gel prepared with heavy water. The results have been compared with the self-diffusion coefficients at microscale obtained by pulsed gradient spin−echo (PGSE) NMR. Both results are in agreement in spite of the complex structure of the gel, but the reduction in diffusion coefficient as compared to bulk water is larger than predicted from effective medium theories.

Optimization of an inorganic/bio-organic matrix for the development of new glucose biosensor membranes

A new mixed membrane material for amperometric glucose biosensors, based on immobilization of glucose oxidase (GOD) in inorganic laponite gels followed by an enzyme crosslinking through glutaraldehyde (GA) is investigated. This method gives the possibility to modulate the enzyme loading in the biomembrane, the corresponding sensitivities obtained being directly proportional to the enzyme content in the membrane. Thus, with a GOD/laponite ratio of 3.3, sensitivities reach up to 132 mA M −1 cm −2 for a linear dymamic range from 10 −2 to 20 mM. Effects of oxygen and temperature have been investigated. The analysis of the bioelectrode characteristics shows a good permeability of this inorganic/organic enzymatic membrane. A specific design, combining a Nafion membrane and incorporation of polyphenol oxydase, allows to reduce the effects of interfering species such as ascorbate, urate and acetaminophen by a factor 4.

23Na Nuclear Quadrupolar Relaxation as a Probe of the Microstructure and Dynamics of Aqueous Clay Dispersions: An Application to Laponite Gels

23Na relaxation studies of aqueous clay dispersions showed influence of the order/disorder transition of clay gels and the quadrupolar relaxation of neutralizing sodium counterions. Detection of the fast and slow components of the 23Na transverse magnetization gives access to the microstructural and dynamical properties of colloidal dispersions. Numerical simulations of sodium diffusion, using a simplified model of clay dispersion, explain the pathology of the 23Na relaxation rates by the high sensitivity of the quadrupolar coupling to the orientational correlations of charged interfaces. Frequency variation of the NQR relaxation rates of confined counterions therefore appears as a new tool for the investigation of the spatial correlations of charged interfaces within disordered porous media.

Microdynamics of exchangeable lithium and sodium ions in laponite gels

Hectorites are natural minerals of the mica family, within the manifold of clay rocks. Organometallic complexes can be inserted within their lamellar structure with interesting catalytic and stereochemical consequences ( Z ). Laponites are synthetic hectorites. They belong to the smectite, i.e., swelling family of clays. Their structure consists of an octahedral layer sandwiched between two tetrahedral layers. In the octahedral layer, all the sites are occupied either by a divalent magnesium ion (trioctahedral clay) or by a lithium ion (one octahedral site in eight). In the tetrahedral layers, there is occasional substitution of a silanol O$iOH group by the fluorinated counterpart O$iF. The counterions responsible for electroneutrality are mostly sodium ions. Laponites exist as platelets about 1000 A in length and about 10 A thick. Their cation-exchange capacity is 50100 meq/ 100 g, about half that of a montmorillonite clay. We have studied laponite B (Laporte Inorganics, Widnes, Cheshire, United Kingdom), whose BET surface area is 330 m*/g and whose cation-exchange capacity is 85 meq / 100 g. Its composition is (percentage per 100 g of clay) SiOz ,55.08; A1203, 0.05; Fe203, 0.06; CaO, 0.20; MgO, 24.82; Na20, 2.55; K20, 0.05; Li20, 1.74; F, 5.6. The interest of laponite for NMR study is twofold: it possesses a rather simple structure, essentially a magnesiosilicate, with an extremely low level of paramagnetic iron impurities, and the water suspensions form gels at high ionic content, due to the binding of the negative silicate planar sheet to the positively charged edges (“house of cards” structure). We have obtained (Bruker AM 300WB and 400 spectrometers) 7Li and 23Na spectra. Longitudinal relaxation times were measured with the inversion-recovery sequence 180”--t-90” followed by a nonlinear regression on the exponential curve, using between 13 and 16 data points. Standard deconvolution procedures were applied to all lineshapes for these Z = 3 nuclei. Theoretical treatments have been provided by Hubbard (2) and Bull (3). Samples consisted of 75 mg of laponite B exchanged with lithium or sodium ions suspended in 4.5 ml of D20. In heavy water, lithium-7 relaxation is quadrupolar (4, 5). The ionic strength was increased by adding the same amount of exchanged clay to aqueous solutions of LiCl or NaCl. The suspension was stirred overnight. Since lithium ions in laponites are either structural or exchangeable, we checked that the high-resolution NMR is opaque to the former and monitors only the latter:

Response of tomato seeds fluid-drilled in low-phosphorus growth media to phosphorus incorporation in the carrier gel

Germinated ‘Heinz 1350’ tomato seeds ( Lycopersicon esculentum Mill.) were fluid-drilled in peat-vermiculite prepared with or without 1.2 kg 0-9-0 m −3 (high-P and low-P media, respectively) using Natrosol 250HHR or Laponite 445 carrier gels containing 0, 10, 20 or 30 g l −1 of NaH 2PO 4, NH 4H 2PO 4 or KH 2PO 4. Percentage emergence was unaffected by P status of the growth medium and was little affected by salt species or concentration in either gel. Emergence rate, however, decreased as gel P concentration increased. Increasing gel P concentration did not increase seedling shoot dry weight in high-P media. In low-P media, however, 10–30 g l −1 of all salts in either gel, compared to 0 g l −1, gave an average 4.2-fold increase in shoot dry weight, with 10 g NH 4H 2PO 4 l −1 gel yielding the greatest shoot dry weight. In a further glasshouse study, germinated tomato seeds were fluid-drilled into low-P media using Natrosol or Laponite gels containing 2700 mg P l −1 as either monobasic (Na, NH 4, K) phosphate salts, or N + P + K salts (KH 2PO 4 + (NH 4) 2SO 4, KH 2PO 4 + NaNO 3, or proprietary 10-6.6-8.3). Low percentage emergence with KH 2PO 4 + NaNO 3 in both gels and with 10-6.6-8.3 in Laponite was associated with high gel electrical conductivity. N + P + K in gel, compared to single monobasic P-salt inclusion, did not give greater seedling growth. The cationic species associated with the phosphate did not significantly influence percentage emergence, shoot dry weight or shoot P concentration. All P-bearing gels gave greater growth and P concentration of shoots than the fluid-drilled (zero salt) control. The 22% greater shoot dry weight with Natrosol than with Laponite was not associated with increased shoot P concentration.

The effect of plant growth regulators and other compounds in gel on the emergence and growth of tomato seedlings in a cool potting medium

SummaryAdenine, gibberellic acid, ascorbic acid, Promalin, PGS-10 and AMP were added to Laponite and Natrosol gels. Germinated tomato seeds were added to the treated gels and incubated for 24 h. The germinated seeds were then fluid drilled into pots and grown in a cool greenhouse at temperatures of 22°C day and 11.5°C night. Emergence and growth of seedlings were unaffected by the gels. Both PGS-10 and AMP reduced the time to 50% emergence compared with the control which was in unmodified gel. Growth as measured by plant height, fresh weight and dry weight was greatest with both PGS-10 and AMP although not significantly different from the control. Promalin (GA4+7 + BA) inhibited emergence and also significantly inhibited plant growth: GA3 stimulated growth. AMP was the most overall effective chemical in counteracting the adverse effects of the cool growing conditions on emergence and growth of tomato seedlings.

Comparisons of the use of pre-germinated, dry and pelleted seeds for block-raising of glasshouse lettuce

The use of pre-germinated seeds for establishing glasshouse lettuce in peat blocks was compared with dry and pelleted seeds. Sowing pre-germinated seeds gave between 1 and 6% higher seedling emergence than from pelleted seeds and between 1 and 3% higher emergence than from dry seeds. Seedling emergence was reduced from 100% to 56% when the seeds were covered with 5 mm of silver sand compared with no cover. Seedling emergence from seeds covered with Agrigel (sodium alginate) was reduced by 24% at a concentration of 0.25% and by 62% at 0.7% compared with no cover. Guar (a natural gum) and Laponite (a synthetic clay) gels also reduced emergence on certain occasions but not by as much as Agrigel. Satisfactory levels of emergence were obtained when seeds were sown into blocks having an inverted, cone-shaped depression for locating the seeds, but the seedlings showed poor root-hair development and had elongated hypocotyls. Normal seedling growth and high levels of emergence were obtained from the seeds sown into blocks having cylindrical holes 10 mm in depth and 5 or 10 mm in diameter. Pre-germinated seeds invariably emerged earlier than pelleted or dry seeds. At low propagating-temperatures (12.0°C maximum and 5.0°C minimum), emergence was 4 days earlier from pre-germinated than from dry or pelleted seeds and 2–3 days earlier at high temperatures (21.0°C maximum and 9.0°C minimum). Coefficients of variation of seedling weight at planting were lower from sowing pre-germinated than pelleted or dry seeds, but these differences were not evident at harvest.