#rheopectic

Non-Newtonian Fluids: Rheopectic vs. Thixotropic

The difference between rheopectic and thixotropic fluids is very similar to the difference between dilatant and pseudoplastic fluids: both are Non Newtonian fluids but while one, pseudoplastic, is shear thinning (viscosity decreases with increased stress) the other, dilatant, is shear thickening (viscosity increases with increased stress). 

But while thixotropic fluids are occasionally mistaken for pseudoplastic fluids, and rheopectic fluids are occasionally mistaken for dilatant fluids, these two types of fluids differ in one crucial way: time dependence. The change in viscosity with respect to stress for dilatant and pseduoplastic fluids is independent of time. But for thixotropic fluids, the viscosity decreases with increased stress the longer the stress is applied. The same goes for rheopectic fluids, the viscosity increases with increased stress the longer said stress is applied. 

As such, thixotropic behavior can be defined as time-dependent pseduoplastic behavior. An example of such behavior can be found in many gels that are thixotropic fluids, almost solid at rest but much more fluid and less viscous when agitated or shaken. Thixotropic fluids return to their original, more viscous state after the stress is no longer applied and when this changes happens nearly instantaneously, the material is essentially considered to be pseudoplastic. 

A more specific example of this is in the so-called 'astronaut pen' developed by Paul Fisher that can write in no gravity. The pen contains a pressurized thixotropic ink that is too thick to flow unless a force is applied - such as the rotation of the ballpoint when writing. 

Rheopectic fluids, which can then be described as exhibiting time-dependent dilatant behavior, are much less common. Examples of materials that exhibit this behavior are printer ink or cream, fluid at first, but becoming thicker when shaken, stirred, or agitated. Much like with dilatant fluids, research is ongoing regarding the use rheopectic fluids in body armor.

Well, I spent a semester studying at the National University of Ireland in Galway and I took an Irish Women’s Poetry class there, so that definitely helps. I just wish I still had my notes, because I can’t remember some of the poets we’ve studied and it’s driving me crazy!

Of course Ireland has a fascinating literary history and a lot of great works by both men and women that focus on themes of colonialism, diaspora, and poverty. However, what fascinates me is how contemporary women poets write against certain aspects of the Irish culture and history and (male-driven) literary tradition. I’m not an expert on Irish history and culture by any means (and you should all feel free to correct me, because my memories of this class are a bit fuzzy), but I remember lectures about two primary themes: religion and nationalism.

You’ve got these two female figures that are basically the pillars of the Irish culture: Éiru, the Gaelic matron goddess of Ireland (the Irish word for Ireland is “Éire”), and the virgin Mary (you should google “Marianism” or “cult of Mary” some time). I hope I don’t have to explain to you why nationalism is a recurring subject, but for those less familiar with the country, it is important to note that the Irish are a very religious people: 84% of the population identifies as Roman Catholic. Abortion is illegal in Ireland, and many hospitals are still run by Catholic religious institutions. Especially in small villages (which is what most of the country consists of, there are only a couple of bigger cities), the church and the parish are still very important institutions. See where I’m going with this?

Strict traditional catholicism as practised throughout Irish history is and was not kind to women and their rights, and when you lived in a small village where everybody knew each other and everybody knew the vicar, it’s not easy to get away from that repression. Poems like Mary O’Malley’s “Cealtrach” give the silent women in Irish history a voice.

Eavan Boland is another poet I absolutely adore who tries to tell the story of the silences. She writes against the male tradition of history and mythology (and is also stellar at articulating issues of colonialism and deplacement, but that is less relevant here). She tells the story of mothers, of daughters, and continuously asks questions about how the past leaves traces in our present and how our maps don’t show the scars of past famines and wars.

So on the one hand you’ve got a culture that venerates female figures, but on the other hand represses and silences them. Writing against that tradition, deconstructing and exposing it, that is what I find so interesting about Irish women’s poetry (in a tiny nutshell).

Unfortunate typo

is there now?