Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange
13

A red gold sol is a colloidal suspension of gold nanoparticles with average size of particles less than 100 nm. The suspension is quite stable — the nanoparticles don't aggregate because of the existence of an electrical double layer on the surface of particles which causes electrostatic repulsion between the particles. If you add a sufficient amount of an ...


10

Please note that I haven't seen the sample myself! However, the Royal Institution claims that a bottle with the collidal gold solution is on display at Michael Faraday's Magnetic Laboratory (see bottle at the bottom of the image) in the museum of the Royal Institution. Update This might be nitpicking and English isn't my native language, but David ...


10

Coagulation is a process which involves coming together of colloidal particles so as to change into large sized particles which ultimately settle as a precipitate or float on the surface. Coagulation is generally brought about by the addition of electrolytes. When an electrolyte is added to a colloidal solution, the particles of the sol take up the ions ...


9

I wouldn't expect the reactions to yield different products but rather different particle size. The higher concentrated $\ce{NaOH}$ should hereby produce smaller particles†. The "solution" in the left vial is probably rather a colloid of microscopically dispersed iron(III) hydroxide. It should show the Tyndall effect if you send a beam of light through it. ...


5

This is classic, the effect is called Mie scattering. Very simply speaking, light is scattered on the whole surface of every (translucent) particle. For round particles, interference makes a diffraction pattern with conic symmetry, i.e. the intensity of diffracted light depends on the angle towards the incoming wave. Obviously the pattern depends on the ...


4

Will this help? Toxicity and cellular uptake of gold nanoparticles: what we have learned so far? Gold has a long tradition as a disease-modifying antirheumatic drug in the treatment of rheumatoid arthritis and it seems to relieve pain and decreases swelling of the joints.


4

Tap water contains calcium and magnesium ions; more so if the water is hard. These ions can bind to soap over time and make an insoluble soap curd. Is the sponge clean? If not, another reason is that the surfactants in the soap that make the foam might be forming micelles around whatever grime is in your sponge, so that there aren't many left to make the ...


4

The micellization releases water molecules which initially solvate the hydrophilic head groups. The release of these waters greatly increases the entropy. Reference: Dong et al., Chem. Rev. 2010, 110, 4978-5022.


4

The short answer to this question is: yes. The movement of particles in suspension like the powder in water would be a perfect example of Brownian motion as Mithoron already said. The particles are being kicked around by the water molecules, which are in constant motion as you already said. This is also true for small airborne particles that collide with ...


4

Cationic micelles similar to your examples can and do exist. For example cetyl trimethylammonium bromide (Growth of Cationic Micelles in the Presence of Organic Additives, P. A. Hassan and J. V. Yakhmi, Langmuir, 2000, 16 (18), pp 7187–7191, DOI: 10.1021/la000517o). Additionally, there are cationic micelle detergents (Ionization of cationic micelles: ...


4

Particles in colloid absorb either positive or negative ion preferentially from solution depending on there surface. This develops a potential on colloid surface called Zeta potential. Due to this potential colloid particles repel each other and can't coagulate. Particle size also play a major role. With decreasing size surface to volume and hence surface ...


4

Words like "homogeneous" and "heterogeneous" do not have a well-defined meaning. Different authors use them differently. The fact is, all matter is made of atoms, and atoms are not homogeneous. Thus, from a certain point of view, nothing is homogeneous. Matter is lumpy! But suppose we don't care about things on the scale of atoms, i.e. angstroms. Then ...


4

The color of conductive nanoparticles depends on plasmonics. In brief, quantum behavior predominates in the few electrons of a nanoparticle, rather than as a continuous conduction band. Surface plasmons strongly influence the color and polarization of light in sols and colloids. For example, for hundreds of years, stained glass has been made with gold or ...


3

A solution implies that there are solvent-solute interactions. Helium is about the most chemically inert atom there is. In the case of water ice, the hydrogen bonding will be orders of magnitude stronger than the van der Waals forces, so colloids will not be stable at 'normal' pressures. I guess if I were looking for a colloid in He(liq), I'd look at N2 or ...


3

The white clear liquid in the egg is nothing but albumin. It helps in supplying nutrition to the yolk and gives strength to the yolk during the formation of chicken. White part doesn't imply whole of an egg. The composition of that white liquid is 90% water and 10% protein. If you dissolve it in water, then it is nothing but a colloidal ...


3

The Royal Institution of Great Britain has a Facebook page, and I shared this question there, hoping they would respond here. Instead they answered my inquiry on Facebook itself. Therefore I am quoting it here: Hi Martin. I'm afraid David Thompson is a little mistaken. We have multiple examples of Faraday colloids with the evidence to prove their ...


3

In order to explain the Schuze-Hardy rule, you have to take into account that you are working with a colloidal dispersions stabilized electrostatically. The stability of this dispersions is well described by the DLVO theory. According to this theory, the particles interaction potential can be expressed as the sum of two contributions, $$V_T = V_A + V_R$$ ...


3

Option (c) is actually correct. Magnesium chloride does coagulate gold sol faster than ferric hydroxide, because ferric hydroxide does not coagulate in the first place. Wikipedia mentions that ferric hydroxide is insoluble at $\ce{pH}=7$, so there aren't any $\ce{Fe^{3+}}$ ions to coagulate the gold sol anyway.


2

According to the wikipedia article on hand sanitizers, polyacrylic acid and polyethelyne glycol are commonly used thickeners. You could try any hydrophilic polymer if those aren't available. Cornstarch might even work if you dissolved it in the alcohol before adding the other ingredients.


2

There are many types of scattering what you are talking about is generically called Tyndall effect. You can "see" the path of the light because some of the photons from the source are scattered in others direction so so they can reach your eyes. But in fact what you see are the photons that don't travel in straight trajectory, so not the beam itself but the ...


2

Light can only be seen when it enters your eye, so it somehow has to find a way between the light source and your cornea. Since light travels in more or less straight lines, it somehow has to change direction if you aren't looking into the source of said light directly. This process is called scattering. It's what makes the path of light visible, because at ...


2

Milk is mostly water, and diluting it (roughly speaking) with sulfuric acid to a concentration of ~50% milk and 50% sulfuric acid will result in a very acidic, but still aqueous, solution. We can examine the likely behavior of other milk components using basic chemical principles. Sugars. Milk is rich a variety of di- and oligo-saccharides such as the ...


2

There are a number of different effects: Rayleigh scattering is the predominant effect for the tiniest particles, much smaller than the wavelength of light, i.e. before they've coalesced. It is dependent on the fourth (!) power of the frequency of the radiation, so short wavelength light is scattered toward the eye. Looking through the colloidal mixture, it ...


2

It depends. if your pH is really high, silicate $\ce{SiO3^2-}$ or $\ce{SiO4^4-}$ ions will form and will become a stable dissolved solute in the solution. if it is moderately high the rate of hydrolysis will increase greatly and the silicon will crash out in the form of orthosilicate hydrates [$\ce{Si(OH)4}$], which may agglomerate to form silica particles. ...


2

This is a question to physics department. Chemists only see liquid helium when refilling NMR instruments. Boiling point and comfort working with changes in this order: He < H2 < N2< NH3 < H2O. I didn't find any papers regarding colloidal systems in N2. So, chances are nobody looked into He yet. Try a deep search on N2 colloids first. Currently ...


2

An emulsifier is a surfactant. A surfactant is characterized by the fact that its molecule has one or more hydrophilic parts and one or more hydrophobic parts. The ratio between the molar mass of the hydrophilic parts and the molar mass of the hydrophobic parts in the molecule is expressed by its HLB value (Hydrophilic-lipophilic balance). Higher HLB means ...


1

Starch in water might work, perhaps with table salt or other bacterial/fungal growth inhibitor. Follow directions in most recipes: mix a bit of starch in cold water and then add gradually to hot water to make a more stable "soup". BTW, blasting a colloid with ultrasound (e.g. from an ultrasonic humidifier) homogenizes it and may delay separation.


1

The molecular basis of osmotic pressure (oncotic pressure is a special type of osmotic pressure) is similar to filtration but on a very small scale. Some membranes are partially permeable: they let small molecules pass but block larger ones. This asymmetry means that a flow of small molecules is created. Imagine things at the molecular level where a lot of ...


1

I dont know why lactalbumin reduces the surface tension but If you know the concepts of surface tension and surfactants then it becomes easier to extrapolate on that concepts to reach the conclusion why lactalbumin reduces surface tension? According to HyperPhysics surface tension is the The cohesive forces between liquid molecules are responsible for ...


1

Metallic nanoparticles, considered as colloids, are attracted to each other by van der Waals forces. To prevent their aggregation, we normally use dispersant using electrostatic repulsion or steric hindrance to stabilize the colloids.


Only top voted, non community-wiki answers of a minimum length are eligible